I get why you are suspicious, the red tones look a bit like makeup. But unless it was a clown or someone with some pretty crazy mixes of colors it seems pretty clear that the browns are dirt and the redder tones could easily be too. And if it were makeup it seems likely that you wouldn't have that mix.
They are also not in a pattern that seems very likely to have come about in the manner you might be imagining and more than anything it would have been very noticeable to your man that it happened and he probably would not have let you find it if it were truly evidence of wrongdoing.
Anyway, that is my take but I'm sure someone who is better about relationship advice will come along and tell you that you need to be able to trust your guy and not hold on to such suspicions if they are thus far unfounded. No matter what the case may be for this if you can't trust your significant other you can't have a lasting relationship. And if he hasn't done anything wrong it would be a pity to doom the relationship due to unfounded suspicion.