Hex Colors in Android are some times 8 digits. How? What is the difference between #FFFFFF and #FFFFFF00

I sometimes have seen in examples where the coloring in Android is done as #FF191919. I mean a 8 digit hex number . But it should be only a 6 digit number. How are they related? If I want o convert a 6 digit number to a 8 digit number. How to do it? I mean convert #424242 to a 8 digit number coloring? Please let me know the details. Thank you for your time and help.

Solution 1:

The extra 2 digits are used to define the colors transparency, or alpha channel.

Android uses the ARGB format (or AARRGGBB as you use in your example)

For more (Android-specific) information take a look at the Color documentation

Solution 2:

The first two characters are representing the alpha (transparency) value, where FF is fully visible. This is known as aRGB.