I bought the white Robox with the intent of altering the color to be more mechanical. I opted for dye since I thought paint would possibly gum up the works, and the robot would lose mobility. After some testing on spare parts, I used RIT Dye More in Frost Grey.
My end result was a 95% success. In an unexpected but promising turn, the joints turned darker and that would save me time trying to detail those. One calf and one forearm turned a slightly different shade of grey with more brown in it; the calf is the most obvious. The functionality was impacted slightly in that the ball joints are very tight now (I suspect the heat impacted the two types of plastic differently), except the head rolls about. I added some mini hold wax to the head joint and fixed that issue. I will add some lubricant to the other joints once my final detailing is complete.
I will add further details and aging, but I am pleased with the results so far. I can work on the mismatched coloration, or perhaps he's had an overhaul or two with not-quite-right replacement parts.
Full post here.