If I have white text in my UITextField, the selection window (when selecting text) is invisible because the background on the little window is also white.
I'm afraid not. The problem's existed since the earliest days of the iPhone OS—white text appears as white-on-white in the cursor-positioning loupe as well. If this is a serious problem for your app, your only real options are to change the text color or to file a radar feature request with Apple.