There are two QuickMask properties you can change by right-clicking on the QuickMask button.
Normally the QuickMask shows unselected areas ΓÇ£fogged over ΓÇ¥ and selected areas ΓÇ£in clearΓÇ¥, but you can reverse this by choosing ΓÇ£Mask Selected AreasΓÇ¥ instead of the default ΓÇ£Mask Unselected AreasΓÇ¥.
By choosing ΓÇ£Configure Color and OpacityΓÇ¥, you can bring up a dialog that allows you to set these to values other than the defaults, which are red at 50% opacity.