Reputation: 28336

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

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 hexadecimal. I just need to insert the hex value into my XAML.

Initially, I pasted the hex value from an email into the appropriate properties. Before I could finish, Blend started having a fit, underlining the color property with a squiggle and a tooltip telling me "Token is not valid." After some research, I found placing a pound sign ("#") in front of the hex value resolved this issue.

In the process of researching this problem, I started changing colors via the color picker in Blend. I quickly found the values Blend was inserting not only started with the pound sign, but also "FF". The values I was pasting were valid colors in a valid hex format. But when entering the RGB values into Blend and letting Blend insert the hex value, I noticed all my colors were prefixed with "#FF". Removing the #, as I already pointed out, generated errors, but removing the "FF" seemed to have no effect at all.

In the world of hexadecimal colors, is the color #5A7F39 really the same as #FF5A7F39? Why the FF? They are two different hex values, right? But they appear identical onscreen. Why the difference?

Upvotes: 6

Answers (3)

James

Reputation:

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.

Upvotes: 0