It happens that way sometimes. Both my parents are brunettes but me and my sister are as ginger as they come. But this time I just think its a model oversight.
It's quite possible to have lighter hair tones or gingerness when parents don't have it. It's the recessive genes appearing when both parents possess it as recessive.
However, darker hair is always more dominant genetically, and it cannot be explained by recessivity.
That being said, it's not an overt two blonde parents producing a black haired kid levels of inconsistent, so I can attribute the slightly darker hair tone to in universe explanation (secondary genetic factors, slightly different eating regimes etc.) or development reason ( DPC just happened to model parents later)
His face is reminiscent of both parents, so that's why that hair color thing is the smallest nitpick. It's just my VFX 3d artist background screaming at my subconscious.
Edit: Part the reason why I think DnG is a waste as a whole, but I'd not remove or replace it regardless, is that it has so many good humorous moments, and as I've stated before, contains my favorite line from the whole game. Sally's sass is black mother levels in there, simply marvelous.
"[ spoiler] i just remembered something... i always assumed that Bela was the Tybalt Harasser but ... the champagne thing both Bella and Jill are occupied with Cathy so... it´s gotta be someone close to him that can´t express their anger... Maybe Rich ? or Stephen to toughen up the boy? Who would care enough about Tybalt to "hate him" most people don´t care! Rusty was with the rest of the gang! Had he a girlfriend one could assume envy of his girlfriend! yeah he seems rich, but that`s not personal enough to create a fake profile out of an emotional response of pure hate!
I think it's Rich. He, like all other VPs in the game, seems to be filling a support column role to the respective presidents. However, whereas Chad has loyalty to his frat, Rusty has both loyalty and affection and support, and Sage interested in keeping the fraternity buoyant as a whole and all sisters to be on good terms....
Tybalt is a selfish, unadulterated idiot who cares for nothing but status. His affection for Jill doesn't present with any genuine affection, (unlike from MC in a proper Jill path), purely out of want for more status. He is living larger than everyone else, for no reason other than he can, and he wants to show off.
Rich's convos with Quinn point out to someone under great stress and emotional pressure. The other preps, other than Tybalt, are more or less agreeable enough fellows, from what the game shows you. (Much like Anthony from jocks.)
Tybalt is actively maliciously destructive against his own fraternity. I can see Rich making calculated decisions to have him removed and restore the fraternity's integrity.
Note 2: Chad and tri alpha's have something they hide with great secrecy, that much has been made clear. And I for one think it's more than some steroid usage. DIK's have that small clique that does regular drug use. HOTs are also involved. And while Rusty and Sage don't seem to take part, they cover for em.
Tybalt is doing nothing of the sort.