I think black soaks up the external heat (as does dark green) which would likely add to the heat if anything.  The black dune buggy motors do look pretty good though, it likely is no benefit, maybe keeps the heat up at idle, I would think.  I think an experiment would have to be done, and it wouldn't be measurable.  I will have to think of an application for the WD 40 treatment.  I think I got one of those heat sensor things somewhere. Probably put in in an oven for a specific amount of time and check the temp. plain and coloured on a heatsink would be a good test.  Oh Hi Wayne.