[stylishgnome]

Why does it turn magenta when you double-click (on two distinct pixels specifically)?

[tikhonj]

That's just the highlight color. Assuming you're using Chrome, it's pretty eager about highlighting random stuff; other browsers may be similar. Try selecting some text.

[VMG]

There is a css rule to disable user selection which might be handy here: http://stackoverflow.com/questions/826782