You can’t just divide everything into black and white.
This comic is intentionally ridiculous to highlight the absurdity of different types of discrimination. Things that don’t make sense:
1) why didn’t the parents realize their son was gray? Perhaps they convinced themselves it was their imagination as many parents do;
2) is their issue with his skin tone or his sexuality? Bisexuals are discriminated against because many people don’t believe they are real. Hence gray refers to the gray area of sexuality that many gay people don’t believe in;
3) you can’t have the DNA of 2 dads to make 1 child (yet).
Discrimination doesn’t make sense.