So as we all know Cory Feldman voiced Donatello in the first film, but was not asked to return for the second film.
(check out the clip at around 3:45)
Bummer right? This clearly done to reshape Donny as a different character trope though. The makers of the second film reshaped Donatello into the Hollywood character trope of (drum rolllllllllll) the token black friend. But not just any token black friend, but the well educated but still urban black friend.
Lets start with the surface level attributes. Donny is a shade of green darker than the rest of the turtles. Some of you will say its just the contrast from his purple mask, but no he is definitely a shade darker than the rest. Just watch the first fight scene in the toy store and the following scene in April's apartment. He. Is. Darker.
Next the persona. So Donny is from NYC, is cool and hip, but is into technology and math. This is the very early 90s so this is extreme nerd territory. Hmmm, wasn't there another character like that? YES. Dwayne Wayne from A Different World!
Donny knows how to goof around, even in dire situation. Look no further than the clown scene. Donny might well be wearing flip up sun glasses and saying "Hey look at that cutie!" But jump to when they are breaking into TGRI and come across a computer who is the first to jump on, Donny. You'd have the exact same dynamic with Dwayne Wayne, Ron Johnson, and Coach Walter.
So there you have it, Donny is Dwayne Wayne. Boom.