I mean, assuming that Adams doesn't do his own coloring, I bet it's just that whoever colors the comics forgot the character was Black. As the article notes, it

I mean, assuming that Adams doesn't do his own coloring, I bet it's just that whoever colors the comics forgot the character was Black. As the article notes, it's literally the first Black character in the strip, and they had been absent for a bit, so it's likely an easy thing to forget.