The text on the buttons next to the login fields cannot be read, because the text is black on a very dark background.
The problem seems to be limited to the classic windows style. I've heard others have it on other versions of windows as well.
It would be solved by giving the buttons an appropriate background colour so that they are not transparant.
It's not related to a minecraft versions, only to the launcher. I've had this issue since I bought the game during 1.7 beta.