My guess on the scarcity of the color black in poker chips is that it was the color of mourning... not the kind of thing you want to think about during a friendly game of cards.

Black borders around death announcements, black clothing at funerals, black armbands, black crepe around the house after a death... these conventions were much more prominent in the first half of the 20th century than they are today.

However, half the cards in a deck of playing cards have black suits, so it wasn't a hard and fast rule [g].