I was about to read a post on Daring Fireball that I had opened in a tab via my news reader, but I really hate dark colored websites. Just reading a few lines will make me see stripes in an afterglow for some reason. I can't figure out why some programmers love light letters on dark backgrounds - like all those Textmate styles you see out there, it just gives me a massive headache, I swear. I can't even look at that stuff without feeling ill.
Which is why one of my favorite bookmarklets is Zap Colors.
Just drag-drop it to your toolbar and use it whenever there's a page who's colors make you ill. All it does is make the text on a page black and the background white. It's awesome, so much so I wish it could be automated like that font-size plugin, so that next time I view that same site, the plain colors would show up automatically. Regardless, it's definitely better than what I used to do, which is use the Web Developer Toolbar to turn off styles all together. This way I still get all the formatting, just not the wonky unreadable color schemes.