Today i read a nice idea on the factorio forums: coal glow red
That would fit the theme of vulcanus a lot I think. Although with your mod now it makes it easy to see, its feels a bit, out of place.
Not sure if you could make it work? or perhaps that just the "edges" of the coal could be grey/white representing a little bit of ash ?

https://forums.factorio.com/viewtopic.php?t=129379

I'm average at writing simple code. But I'm a bad artist. I'm afraid I won't be able to make a decent texture for this, sorry...

Thanks for your reply. I wonder will this mod also chain the coal ore on nauvis?

Unfortunately, yes. Coal uses one texture for all planets