Did "white" in "decent white folk" originally refer to race?
Solution 1:
'Decent white folks' in Google Books
The earlier and more common wording of the phrase seems to be "decent white folks" (plural folks), as this Ngram chart of "decent white folk" (blue line) versus "decent white folks" (red line) suggests:
A quick look at the related Google Books search results Google strongly suggests that the word white in the phrase has always referred to "white race." The earliest instance of either phrase in the search results is from Edmund Kirke, A Merchant's Story, serialized in The Continental Monthly (November 1862), which uses the phrase in the context of a starkly racist comparison:
'I shall go when I please—not before,' said Mr. Gaston.
'You'll please mighty sudden, then, I reckon. A young man of your edication should be 'bout better business than gittin' inter brawls with low groggery keepers, and 'sultin' decent white folks with your scented-up niggers. Yer a disgrace ter yer good ole father, and them as was afore him. ...'
The next-earliest match for either phrase is from Benjamin Lloyd, Lights and Shades in San Francisco (1876):
When once they have planted themselves in a building, the Chinese rapidly take root; and although they do not manifest any stubbornness by refusing to vacate the premises, experience proves that they make themselves masters of the situation, and are seldom dispossessed. They simply make the building uninhabitable for decent white folk. Their manner of living accomplishes this, without any extra precaution on their part. They will divide the rooms into numerous diminutive compartments by unsightly partitions, and the smoke and rank odor from their open fires and opium pipes, discolors the ceilings and walls and renders the whole building offensive, both to sight and smell, so that the expense of renovating it would not be offset by the rental receipts for six months or a year.
And the third-earliest match is from Joseph Jones & May Wade, John's Alive: Or, The Bride of a Ghost, and Other Sketches (1883):
"Now, I'll stick you with opening the door, won't I! Go home, I tell you! If you was any kin to decent white folks you'd be ashamed to disturb anybody so. But you may stand there and bawl till you're tired. I'll not let you under my roof, that's what I won't."
This last excerpt is from a story set in northern Florida, and the old woman who speaks the quoted lines later accuses the marshal and his deputies (whom she is refusing to admit to her house) of being "white Ingin devils."
So in the earliest three Google Books matches we have "decent white folk[s]" being cited in contrast to blacks, Chinese, and mixed-race Native American Indian/white people.
'Decent white folks' in old newspapers
A search of the California Digital Newspaper Collection finds a slightly earlier instance of "decent white folks" than the first of the Google Books matches cited above. From "Letter from New York" (July 16, 1860), printed in the Sacramento Daily Union (August 2, 1860):
An ominous silence fell upon the party [of gentlemen including Dr. Bradford] as Lawrence [friend of a man whose wife Bradford had insulted] stepped into the ring. There was good reason for it, since his first act was to face Dr, Bradford and remark to him, with a number of expletives more energetic than pleasant superadded, that he (Bradford) was a villain, etc., etc., and it would give him (Lawrence) sincere pleasure to blow him to that sulphuric region for which he (Lawrence) considered him much fitter than for a residence among decent white folks.
The Library of Congress's Chronicling America newspaper database finds three matches between 1863 and 1872. From the Daily Evansville [Indiana] Journal (September 18, 1863):
There are several things wanting on the O. & M. [train line]—a better laid track—cars that will do for decent white folks to ride in, in lieu of the present most loathsome ones, and, I was going to say, better conductors and regulations, but this would throw things out of proportion.
"McClellan Democracy," in the [Marysville, Kansas] Big Blue Union (May 28, 1864) has this rather blatant forgery attributed to a political enemy:
The Erie Gazette says, an enthusiastic Democrat, determined to make General George Mellen, Muller, or McClellan President, had the following handbill posted in one of the lower counties. The orthography is admirable, and to gratify a "constant reader" it is given verbatim in the columns of the Gazette:
PUBLIC NOTIS
A meeting will be held in the tavern of James Keeler Phoenuckvil for to go in faver of Gen Geo Mclelan for to be president next election and in favor of stopping the war all in favor of stopping abilitions from kilin decent white folks are specially invited to be present on the occasion as several speakers will be present Rally Democrats and show the abolitioners that we are bound to put Mellen (gim Mellen) through.
And from "Advice to the Colored People," in the Donaldsonville [Louisiana] Chief (July 6, 1872):
One thing the colored people must learn if they intend to stand on the same platform with white folk, and that is, that dishonesty degrades a man. The negroes must quit selling themselves for money. ... The colored people know who their managers are, and they know that these men can be bought and are bought as often as necessity for their purchase arises. This is not only disgraceful in those who sell themselves, but it is disgraceful in those who support the man who allows himself to be bought. When a white man gets that low in his conduct decent white folks refuse to have anything more to do with him.
In all of these examples, "decent white folks" seems primarily to be used as a point of comparison to other white folks who may be less savory. There isn't the same comparison between "decent white folks" and people of other races that animates the three Googles Books quotations—although there is something deeply ironic in the Louisiana newspaper editor's attempt to instruct black readers, less than a decade after emancipation, about the importance of not "selling themselves for money" (to say nothing of the irony of instructing them on how to behave "if they want to stand on the same platform with white folks," shortly before segregation became the de facto law of the Southland).
In any case, "decent white folks" seems to have referred from the outset to Caucasians/European Americans/white people, and not figuratively to white in a sense such as "virginal" or "sanctified."
Solution 2:
Sven's excellent answer covers the main answer very well, 'white' is and has been a politicized term of exclusion. But I would add a slight addendum that (particularly in America) the designation 'white' had historically been a much narrower category than it is now.
For example in the United States there was a time that various European ethnicities were labelled as "colored" in legal documents.
That author's main article is one of the best descriptions I've seen of the way that the legal usage has changed over time.
Wikipedia is always a poor reference in itself, but it provides a decent generalization of what you might find in various historical contexts:
The definition of white has changed significantly over the course of American history. Even among Europeans those not considered white at some point in American history include Southern Europeans (Italian, Spaniard, Greek, Portuguese, etc.), Irish people and Central Europeans (Germans, Poles) and Eastern Europeans (Russians) but mostly notably[citation needed] Polish people due to the Partitions of Poland.[31][32]
In any context, in any country "white people" has always been a BS political football used to diminish the rights of others on a basis of ethnicity. It is particularly egregious in its flexible willingness to adopt previously exempted groups, and redirect them against the remaining non-privileged ethnicities.
Footnotes on some cited newspaper references:
In the First item that Sven could find { "Letter from New York" (July 16, 1860), printed in the Sacramento Daily Union (August 2, 1860)" } The target being called "not decent white folk" is a Caucasian male (see the full article).
In the second example { From the Daily Evansville [Indiana] Journal (September 18, 1863) } the individuals referred to as bringing down the atmosphere are also not ethnically African, Asian, Native American etc. as they would not have been allowed in the general public carriages spoken of.
Does the fact that these two citations are dealing with political and economic contexts make the term any less "racial"? No, if anything it's an even worse degree of racism, because the implication is that a person's low state or political party "makes them almost as non-human as if they had been born black".
{Interesting the third citation which IS talking about negro Americans includes the phrase "When a white man get's that low in his conduct decent white folks refuse to have anything more to do with him" as a political form of pressure to shame black voters.}
Solution 3:
The adjective good meaning “possessing or displaying moral virtue” used in conjunction with “white folk” is far more common than its related synonymon decent. See the Ngram chart below
Examples of good white folk in literature
- But also there are poor whites, plain crackers, and the good white folk. (1942)
- “Are they honest and kind?”
“Oh, yaas, ma'am —dey'se good white folk”
“Good white folk?”
“Oh, yaas, ma'am — course you knows white folks will be white folks — white folks will be white folks. Your servant, ma'am.” (1911) - Good Negroes and Good White Folk (1934) [emphasis not mine]
- But the good white folk of Montgomery are furious at putting such ideas of well-being into the heads of "niggers," especially because the government is installing running water. (1936)
- He might act the part, but it was always an act put on for the consumption of the good white folk present. The Negro has never been half as dumb as his white friend believed him. (1942)
- "... when Indian come to this place with his skins and peltry, very good ; white folk very kind to Indian, plenty good food to eat, pay Indian good money, and whatever Indian ask for his goods." (1878)
Comparing the plural noun phrase good white folks (blue line) with the singular good white folk (red line) and decent white folks (green line) we obtain the following Ngram chart
Examples of good white folks in 19th century literature via Google Books
There are some good white folks and nice ones too. I had rather go to a white persons house any day than an Indians house (1891)
By this time we were surrounded by the evening shades, and repose demanded an end to the present interview— informed Frank, that it was the custom of good white folks to pray to God, before they went to sleep (1855)
The following extract comes from a book containing a collection of popular songs of war, sentiment, humor and ‘olden time’, it was printed in New York in 1865.
Song: The Ham Fat Man
From this random selection of citations there is nothing that suggests the term white in ‘good white folk/s’ or ‘decent white folk/s’ never referred to race. In fact, it was often used in juxtaposition with people whose skin colour or origins were neither white nor European. It's no coincidence either that all the aforementioned citations are from North American publications, reflecting a period when racism was at its most rife.
To test this further I compared the white folks with the previous noun expressions, and Google Ngrams produced this result
Examples of “the white folks” from 19th century literature
- The black folks said that if the white folks would take care of him it was all right. On Monday morning the white folks came and got this white man, saying they were going to carry him to Bellevue. (1870) link
- The negro replied, “ I don't know, master, but the white folks say I belong to his children.” Perry must have been a stranger to Hines, or he would not have asked the negro about the title. (1867)
- If the white folks, our masters, ever get to heaven, they will have learned, before they get there, to love all their fellow creatures, white and black, as themselves ; and when they see us there, too, if we ever are so fortunate as to get there, they will love us as brethren and equals, because God regards us all in that light, and because we are such.” “Well, den, I b'lieves that many of de white folks won't go to heaven, becase we is to have a seat dare, too. They'd rather singe and roast in hell, alone, than enjoy heaven wid de niggers. Dats what I think....”(1858)
- Sister Nancy was very much obligated by the fan and basket Miss Neely sent her, and was in a great maze at niggers doing any thing so tasty ; and they were all astonished when I told them how the white folks buy what the niggers make, and what a laying up they can git if they have a mind to, just from knick-knacks, and eggs, and potatoes, and so on. (1838) link
- ... until just nearly dusk, and a man, Madison Bell, a colored man, came and says, “Mrs. Caldwell, you had better go down and see about Mr. Caldwell, I think the white folks will kill him ; they are getting their guns and pistols, and you had better go and get your husband away from town.” (1836) link
Conclusion
There is nothing which suggests that white in “the [good/decent] white folks” ever referred to anything other than the white "race". I would be very interested in knowing from which source the OP received this impression or interpretation.