As Maniac meets more people, he sees that not everyone is "color blind" the way he is. Why is Maniac "color blind?"

There is one quote that I love that seems to really nail Maniac's "color blindness."  The quote is from chapter 16.

He didn't figure he was white any more than the East Enders were black, He looked himself over pretty hard and came up with at least seven different shades and colors right on his own skin, not one of them being what he would call white (except for his eyeballs, which weren't any whiter than the eyeballs of the kids in the East End.)

Which was all a big relief to Maniac, finding out he wasn't really white, because the way he figured, white was about the most boring color of all.

I think a large part of Maniac's color blindness is the fact that he doesn't see himself as a single color.  When he looks at himself or other people, he doesn't see single colors.  He sees a bunch of different colors at the same time.  To Maniac, calling somebody a single color is just silly.  

I think another reason that Maniac is color blind to skin color is because Maniac judges people for what they do, how they act, and how they treat other people.  Maniac's vision is deeds based, not skin color based.  That's why Maniac wasn't suspicious of Mars Bar until Mars Bar pulled a massive mood swing on Maniac for taking a bite of the offered candy bar and hit Maniac.  Maniac judges people for how they treat him.  Black and white people have both been mean and nice to Maniac, so Maniac doesn't believe skin color has anything to do with.