[L473ncy]

This might be a noob answer but what's the switch made of? If it's metal you might be able to anodize it.

Otherwise I believe there are inks and paints that will actually eat INTO things and make the colour relatively permanent.

Other way that (I think) will work is to "drybrush" a colour onto the switch, take a fine brush, get some paint and "dry" it using a paper napkin or something so that theres still paint on the brush but it's really dry and just quickly go back and forth over the switch, it should really stick to the edges of the switch.