If it is not scabbing or crusting, it might be normal for this breed. The cat will not lay on the heater until it actually burns if it is a healthy cat, so I highly doubt that is the problem. If you are seeing pimples or scabs, its more likely to be an allergy which this breed is prone to. Darkening of skin can occur as cats age, but is seen more readily in hairless cats. Hormonal diseases such as hyperthyroidism and cushings (rare in cats) can affect the skin this way, but you would see other signs of disease.
My guess is that this is normal. If it doesn't seem to irritate the cat, just leave it be. Just keep an eye on it, and if problems, let your vet know.
If you feel my answer was helpful, please click on ACCEPT. Feedback & Bonuses are always welcome. If a deposit has been made, it remains with Just Answer until you press ACCEPT. Once you press ACCEPT then I am paid.
If there is something I can further clarify, Click REPLY. Our dialog continues even after you click accept, I want to be sure your question is fully answered.
Cat Veterinarian
20 years experience in Veterinary field.