The behavior of the buttons in the flash player - need help

I am developing a flash player design, as a result of which disagreements arose with the project manager on some issues:

1. Should the “play”, “full screen”, etc. buttons be be highlighted when you hover the mouse, or is it enough that the button changed only when you click?
2. Similar to the slider on the scroll bar - should it also be highlighted when you hover with the mouse, or change only when it is used directly?

Each of us is on our opinion.
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I wonder if there is any usability rule about this, or is it all a matter of taste?