what ever ingva.
we have word gal, galj meaning black.
we have ugalj, ugolj, uglj, uholj which all mean coal. we know that first coal was charcoal where wood is turned black (gal, galj) and becomes ugalj = u + galj = coal.

It doesn't really matter if the word was originally vu galj which turned into u galj.

we also have irish, and english words for coal which feature both g and k.

we also have words:

ugljen, ugljenisati – to turn into coal, charcoal
ugljevlje – chared wood

If you can't see this, you are blind. Or just plain….

What is most amazing is that you can't see significance of all this. Gal meaning black and crow, raven exists only in Slavic languages. How it got into Slavic languages we don't know. But it is only preserved there. Which means that Gal, Gali, Gallia was the name given to Celts by their (Proto) Slavic neighbors…

But again I am not surprised by this at all…