color lib

[Andrea Fontana via Digitalmars-d]

On Monday, 10 October 2016 at 23:26:53 UTC, Manu wrote:
> I'm not sure why it matters what format the colour you have 
> is...
> Strings are in the form #RRGGBB, or #AARRGGBB. That is all.
> It's the standard I've seen used everywhere ever, including the 
> web,
> which is a pretty good precedent :P

If the web is a good precedent (CSS4 specs):
"The first 6 digits are interpreted identically to the 6-digit 
notation. The last pair of digits, interpreted as a hexadecimal 
number, specifies the alpha channel of the color, where 00 
represents a fully transparent color and ff represent a fully 
opaque color."

https://drafts.csswg.org/css-color/#hex-notation

CSS3 doesn't support hex string with alpha but they suggest you 
to use rgba() function. I think argb() doesn't exists instead.
https://www.w3.org/TR/2011/REC-css3-color-20110607/#rgba-color

Chrome 52 supports it:
https://googlechrome.github.io/samples/css-alpha-channel/

Android instead:
https://developer.android.com/reference/android/graphics/Color.html#parseColor(java.lang.String)
"Parse the color string, and return the corresponding color-int. 
If the string cannot be parsed, throws an 
IllegalArgumentException exception. Supported formats are: 
#RRGGBB #AARRGGBB [...]"

Please notice that on PNG file format rgba is quite common (also 
on bmp with semi-official apha support)
PNG: http://www.libpng.org/pub/png/book/chapter08.html