My understanding is that the green pcb was prone to having quality issues with the solder points, but that they increased the quality control on those and that carts from later batches should not have the problem. The new black design is apparently not prone to the solder problem at all. I have a green one from way before the problem batches that still works just fine.
@Silent Storm: I assume that if you have problems they'll replace it with whatever they have in stock, which would be the black pcb.
-Bri