I don't know what made me think of this today, but I remembered when I toured the University of Evansville Theatre Dept. They had some neat home made lights for running lights. They were a standard 75-watt(ish) bulb in a screw base. The base was mounted on a square piece of plywood. Over the top was a top and four sides. (So it was a cube... 8"x8"x8" roughly.) The top was just another piece of plywood (with a few small holes for venting.) The sides had holes in them with a gel frame in a slot in front. If they didn't need light coming out of one-two-three of the sides they would just drop a mirror or a piece of plywood in the slot. To provide a darker look, they would have a blue or a red gel in it.