We started out with a couple of cabinets we'd gotten from Ikea well before Alex was born (I think it's the Yinden-svorden-bergstrom-leheuden-borkborkbork cabinet, now unavailable), but painted here and there with a few primary colors. And as soon as he could pick up a pen, pencil, or marker, Alex embellished them with his own contributions. Here's one of them.
There were also a few makeshift shelves (just a plank and some brackets), painted a bright red to contrast with the blue/green walls, shown here after the room was repainted.
For the cabinets, the fairly obvious thing was to paint them in suitably Batman-ish black and gray. The lighting makes the darker gray on the lower cabinet appear bluer than it really is; there's also a bit of texture in some of the paint that doesn't come through here.
I was going to do the same thing to the shelves when I thought of the way the Justice League and related DCU cartoons, particularly Batman Beyond, depicted ultra-tech computer systems.
So instead of completely painting over them, I taped a bunch of lines to mask the original red in interesting patterns.
Paint, remove tape, remount shelves.