What's the etymology of "Blue dollar"?

Solution 1:

From Spanish Wikipedia - Dólar blue:

Según algunos periódicos, el adjetivo blue se debe a que las transacciones que se realizan con este billete provienen del mercado negro, por fuera de la regulación establecida por la AFIP y en inglés el color azul también es utilizado para hablar de algo oscuro.

Translation: According to some newspapers , the adjective "blue" is because transactions done with these bank notes are done on the black market to skirt the regulations established by the AFIP and, in English, blue color is also used to talk about something dark.

Solution 2:

It refers to an informal, parallel or black market (informal, paralelo o mercado negro) where people may exchange pesos for dollars.

I think the term blue may come from the national flag colour to refer to "argentinian dollars", exchanged outside the official currency market at a rate accepted only in Argentina.

The national flag of Argentina is a triband, composed of three equally wide horizontal bands coloured light blue, and white:

Blue dollar:

• Slang. In Argentina, the nickname for the black market rate for the U.S. dollar, which is significantly higher than the official rate.

Blue dollar

• a euphemism for the black market for U.S. dollars in Argentina. The blue market developed after President Cristina Fernández de Kirchner and her administration placed restrictions on the purchase of dollars in 2011. Today, dollars are only sold for travel outside the country and require documentation to AFIP, the country’s tax agency, before the purchase is permitted.[iv] The exchange rate in the blue market, however, runs substantially higher than the legal exchange rate, peaking at almost double the legal rate in May 2013. The price for the blue dollar is also extremely volatile, in part reflecting the existing economic and political climates of the country

Another assumption is that it derives from blue money from to blue, a slang expression that means to blow money:

to blue (v.2slang)

Also blew.

• trans. To spend or get through (money) lavishly or extravagantly; = blow v.1 9 c.

As in:

• 1846 Swell's Night Guide 76 The coves..vot we blues a bob or a tanner to see. 1859 Hotten Dict. Slang. s.v. Blewed, ‘I blewed all my blunt last night’, I spent all my money.

• 1867 T. W. Robertson Caste 111, ‘So Papa Eccles had the money?’ ‘And blued it!’ 1884 Daily Tel. 28 May 5/1 He took to horses, and blewed the blooming lot [i.e. {pstlg}1,700] in eighteen months.

• 1888 Farjeon Miser Farebrother III. i. 5 You brought down two thousand pounds with you, and you blued it.

• 1930 W. de la Mare On Edge 228 She had taken a holiday and just blued some of her savings. 1959 Observer 17 May 8/5 Men in cotton shirts and corduroys met there to ‘blue’ their cheques on supplies and on fiery colonial rum.