Or it could have been a minority artist that thought "The only character not wearing a ninja outfit and showing any skin is the janitor, I'm gonna use this opportunity to make him dark skinned like me" and it just went horribly, horribly wrong.
Unlike with the Red Cross pool safety poster, I can't imagine how this WASN'T intentional. I'm not saying that everyone who saw this understood the implications and let it slide. But the person who made it had to know what they were doing. What would be the reasoning for just the janitor to be brown?