It seems that some old and new style bugs have cropped up with the various style changes that have occurred over the course of 2011.
Which is, well, all of them? :)
Let's take a look at the tag wiki editing page:
The contrast of all of the text directly on the page is too low, the color could stand to be darkened.
The text color of the full preview absolutely needs to be fixed.
Additionally, could the character counter text for the excerpt field have a little bit more room to breath?