Well, I'm still stumped. I've been doing some research, and can't come up with anything. The info on feline Lyme disease I read doesn't mention spots. Ringworm is still a possibility, I suppose. If it is, you'd think there would be some hair loss and itching. I hate to tell you your cat's all right and be wrong. But I suppose if the behavior, eating, etc are all normal, it should be OK to just keep an eye on it for a few days and see if it gets worse or not. If it doesn't get any worse or affect him physically you might be all right waiting until next month. Maybe it's just some normal skin pigmentation that's just now starting to come out, are some change in hair color. Maybe this evening someone who knows what this is will come across this topic and post an answer. I left a post in the "Health" section redirecting to this, also.
I edited this to add that if it is ringworm, that's something you want to get taken care of pronto, not because it endangers your cat's life but because it's so problematic getting rid of the fungus spores once they're spread all through your house.