Why is there a leading “#FF” in hexadecimal color values?

Question

I\'m using Expression Blend 3 and am writing some of the XAML by hand, specifically the color values of controls.

I have a list of RGB colors already converted to hex

Answer 1

That may be the alpha component of the color, which represents the opacity (00 -> transparent, FF -> opaque).

MSDN seems to agree with this: Color

16-bit hexadecimal, alpha -- #AARRGGBB

Answer 2

The 'extra' FF is an alpha value (degree of transparency). If you only have three hexadecimal pairs, the alpha value is assumed to be ff (no transparency). However, if you compare #335A7F39 and #FF5A7F39, you should see a difference.

Answer 3

I believe the leading FF is the alpha. 255 (or FF) being 100% opaque, and 00 would be transparent.