Tested in recent versions, including 2.0.0.686

Eh, this isn't really a "bug", more of a side-effect in the case that both colours are the same. The colours could be changed on the biomes themselves so they aren't the same, but it doesn't really matter all that much really.

Believe this ended up being a Forge bug that has been fixed, but i'm closing it regardless whilst i clean up the issues section.