Any extension that lets me change the forum font colors there?

[deepndark]

I googled for changing colors for the forum fonts and found a thread from 2012. I think it still may mostly be the same in 2019, but, if there's an extension for that, I'd sure want to give it a shot. The thread from the 2012: viewtopic.php?t=2151490

Anyway, if this kind of extension doesn't exist yet, I'd want to request for one.
I.E. An extension to change all the forum font colors there are.

Thank You!

EDIT: If I want to change all the font colors on my forum that are grey atm. and the same kind of grey ones, do I still need to change every color separately then in the colours.css?