When I select a color field and the small color window pops up and I try to resize it so that I can adjust the alpha field the window is closed. Sometimes I get a log message about onGUI not cleaning up correctly.
This has been discussed before - make sure you are using the latest version as it was a bug in a previous one...
You should provide more information about your setup so that the development team can pinpoint the problem and fix it in the next build.
This is definitely a duplicate report. All spawned small 'tool' windows cannot be resized and disappear.