It’s because the ver looks like vert which is the french word for green

Vermont is derived from Green Mountain

So vermilion looks like it could mean a green million, which sounds like a funny way to say a million dollars.

Verde is also green in Spanish. A quick translation tells me that in Latin it’s Viridis which makes it make sense that it’s similar in most Latin based languages.

A fancy word for green in English is Viridian