Re: Tired plastic
In my view, most of these oil based suggestions will make a faded bumper a bit darker - as though it was wet - and then gather dust. Back to black et al have some pigment which darken the plastic but rub off on you clothes. In my experience, plastic paint looks good for a while but eventually cracks and peels off.
I have just changed some red vinyl seats to satin jet black using a product called VHT Vinyl Dye which also seems to work on hard plastics. They claim that it actually penetrates the material and 'dyes' it rather than being a surface layer which will crack off in heat or when flexed. Only time will tell how long it lasts, but looks good at the moment.
It only seems to be available from Frost Auto Restorationsin the UK.