It does seem to be a bug. Present when trying to change background and text colour.
Not sure I can reproduce.
The color picker only applies the color once you click OK, there is no "Apply" button that would apply the color on the fly without having to go out of the color picker.
(at least for me, using the color picker of Windows 7 ?)
Im using Chrome on Mac and I cant see an "OK" or "Apply" button.