[@Mahz]:
The RP tabs appear to have the same shadow effect as the white text on, for instance, Quote and Mention buttons. Since both the text and shadow are black, the text just turns slightly fuzzy, or smudged. 
[img]http://picload.org/image/cwaawiw/tabs.png[/img]
I did stare at those a bit before I figured out what was off (and that my screen wasn't failing at delivering a clear text, somehow).

Zooming in makes it more apparent now that I check; perhaps I should also fetch you a maximum-sized example.