When I paint over colors, they don't blend as if paint, like usual. They do this weird... burn-like thing, it seems, and I have no idea why. And the layer is set to Normal, so I know that isn't an issue. I've also tried it with several different brushes, but that doesn't seem to be an issue either.
Also, I've always had this issue where when I save something in PS, when I upload it to the web, it looks considerably lighter than what it does in the program.
FYI, I'm using CS3.