Fix colors of disabled spin buttons (and maybe others)

Fix colors of disabled spin buttons (and maybe others)

The insensitive state should not get a base color that's the same as the
enabled one, or the difference is not visible enough (only the text
color changes). In fact, since the goal of the entry modifications is to
aid visibility during user input, there is no reason to override the
insensitive colors.

Just inherit the insensitive colors of the global style.

Also fix a comment that was attached to the wrong declaration.