Sometimes you want to be able to quickly fill in gaps in line art, for example to make flood-filling easier. Here is one way to do it, which works in most current graphics applications which support layers and selection operations. I use it both in Adobe Photoshop and in GIMP.
How can you be sure that the colors on your monitor are the same as the colors on other peoples' monitors? You can't! But if you want to come as close as you can, try calibrating it using these handy instructions!
Last updated September 2, 2010, because some of the information has become horribly outdated since the last time I touched it back in late 2005. There's probably a lot of other historical crap anyway but I can't be bothered to rewrite this page.