I'm using trial version of photoshop to paint a GIF file. I select #FFFFFF (pure white) and then select brush to color my picture. But the color that's painted on my picture is #F0F0F0. Why is it not #FFFFFF?
To expand on that a little - this happens because a .gif or .png optimizes it's file size by storing only the colors used in it's lookup table. So if you have, say, an indexed color image (a gif) with only 32 colors, it doesn't have the other 224 colors in it's lookup table.