Make your graphic icon into a movieClip, then attach something like...
onClipEvent (enterFrame) {
if (_alpha>50 && this.hitTest(_root._xmouse, _root._ymouse,true)) {
_alpha-=5;
} else if (_alpha<100) {
_alpha+=5;
}
}
...which will fade the graphic down to 50% transparency depending on how long the mouse sits over it - when you roll off the graphic will gradually return to normal.
Changing colour can be done with the same mouse detection piece, just substitute a Color() object script for the _alpha stuff (bit more complicated but not a major problem).