Not sure whether I can edit the title, but I've solved my problem.
I added this code into my colors.xc file
If anyone else is trying to replicate this, the colours that "def.colorRating.X" is referring to are defined at the top of this same file, found in \World of Tanks\res_mods\configs\xvm\Aslain. I don't remember what the default colours are called, but the easiest way to do this is to just copy another section from the same file, for example the win rate section, and just rename it to the damageRating section. You don't need 10 entries in the scale, I just modified Aslain's colour scheme myself to have a 10 colour scale.
Thanks for the help, Grandorf.