I choose "miscellaneous".
I think they (the subwoofers) are perfect the way they are. K.I.S.S. Black. Simple. Make boom.
OR
Go for the extreme ... custom paint jobs. Like a spider-man web motive in black and red. And dark red neon under carriage lighting. That would look sweet. Another one would be a dark blue pearl coat finish, with a volume sensitive light cluster lighting up to the beat.