1.3 Spoilers: Enhancing the User Interface

[Brendan D. Winter]

Actually... if it was painted, then the dirt itself would be coloured too, and not the grass alone. While it's safest to assume it's painted, it doesn't rule out the possibility that there is in fact a new biome upcoming. Perhaps it's the crimson/corruption counterpart for the Hallow, I heard people talking about this a while ago.

You can paint the grass alone, just don't use a deep paint. Try painting it with normal purple or normal red.