In 1.12.2 chromablocks-1.0.jar,

The en_us.lang file has the name for the Green Chroma Block as:

tile.chromablocks:chroma_Green.name=Green Chroma Block

Instead of all lower case causing it to not register properly.

(Needs to be tile.chromablocks:chroma_green.name=Green Chroma Block)

This can also be fixed with a resource pack or resource loader or editing the jars assets manually.

But fixing this on your end would still be nice for those using the mod who don't know how to fix this themselves.