re: Should I paint vent covers the same color as my light fixtures?

Ugh, no. If the vent covers are on walls or ceilings, they should be painted the same color as those walls/ceilings. Light fixtures are decorative elements, not functional necessities. I also dislike decorative switch plate and outlet covers....those should be unobtrusive as possible, painted or selected to match the wall colors.

Too many small, high-contrast "decorative" details clutter up a room.