See:

• Website colors are wrong
• Websites look wrong or appear differently than they should

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

• Don't make any changes on the Safe mode start window.

See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

I only HAVE the default theme! Pages look the same in Safe Mode...no bkgrnd color...

The plot thickens...now my McAfee Security Center is getting the same way...plain-text-ish...???

I think I finally may have solved the mystery...Windows FINALLY brought up a message saying I need to enlarge the max. size of my registry...we'll see if it works...

Did you check the other (Windows) causes for this issue?

See http://kb.mozillazine.org/Website_colors_are_wrong

Apparently it was because I had used Magnifier the other day to try to make something out on a picture...thanks!

( Start Menu -> Control Panel -> Accessibility -> Display -> uncheck "Use High Contrast")

THANKS, THANKS, AND THANKS AGAIN!!! I have spent the last 2 months trying to figure out what the heck was going on with my computer. Well, this step helped to solve my issue (uncheck high contrast). What a relief! Did I say thanks? LOL

yes, unchecking high contrast fixed my problem too on my hp mini - thank you so much - two days of --------- around ....