It happens to my black cat too, but don't know if the red/gold recessive gene theory also works for moggies??
I have always put it down to the sun, but who knows...
When Dill gets fluffy, his fluff is more of a reddish colour, not rich chocolate..., is that due to a recessive gene?? There were two red/golden ish pups in his litter so I suppose it is possible...