Art student Danielle Pecora from the Pratt Institute in Brooklyn designed this ball to help children learn how to read Braille:
Looking a bit like a stiff Koosh ball, it has 26 magnetic pegs, each depicting a letter of the alphabet in Latin on one side and Braille on the other. The object's to fit the pegs into 26 circular indents in the ball that are themselves embossed in Braille letters. "A" in Braille, for instance, is a single dot, so you'd find the peg with one dot, then match it to the spot on the ball with one dot. An electronic device in the ball chimes when you get a letter right. It'll also verbalize what letter you're touching when you run your fingers over the indents.
Link | Photo: Pratt Institute
Also, colors are a good idea, because kids with low vision can often identify contrast, like black and yellow or black and white.
If you look at the pegs, you will see a raised ridge along the side. It is probably an orientation line.