Color Theory, File Formats, etc.
Charles A. Poynton has published a goldmine of color information on his Color Technology site.
What Is.COM's list of every file extension known. Descriptions are sketchy at best, sometimes incomplete or wrong (ACL = Corel Draw 6 keyboard accelerator file? Maybe, but how about Access Control List?)
There's lots of other interesting info on the main Whatis.com site.
The descriptions are more complete at Wotsit.org and quite a few of the file format entries include links to detailed format info. But alas, the site has some *really* annoying ads and popups. The price we pay ...
Niles Ritter's Unofficial TIFF Home Page contains links to all the official TIFF sources and tons more info.
There's a free Photoshop plug-in at vischeck.com that allows you to preview your images as a person with any of several different forms of color blindness might see it. And just in case you're in any doubt, you can test your own color vision here