Kind of surprised that seemingly no one offers these grips in anything other than black. I'm kind of leaning toward that tan leather look, but the gray ones give off a nice "industrial" sort of vibe. I'm sure they could be molded in color but most vendors probably don't want to fool with that. The black ones they're already selling are being used to repair damaged grips and not to people looking to redecorate their camera.
My grips are still in good shape, but there are some paints and dyes made to work on rubber. If I could find the type of material the grips are made of I might get some of the paint, buy a set of new grips and do some experimenting. If the paint didn't bond well it wouldn't be worth messing with.