Websites turn pink in Firefox

I don't know when it happened exactly, but over the last couple of days I have noticed that some websites have turned pink in my browser. Most notably, my Google Reader is now blue, white and pink.

Even the websites I have created myself are now part pink. It doesn't happen in IE, only in Firefox. The color settings in Firefox are just fine, the default background color is still set to white and I have tried resetting it to no avail.

I have no idea why this is happening and searching turns out only like two other people with the same problem, but no resolution.