On this thread you may be able to find some solution or workaround – workaround because people use callouts with highlight colour HEX code information.
In the post I am referencing and before it, there is talk of matching up the colours of those of Zotero’s highlight colours. Not sure how much it’ll help.
If you feel bogged down for more than an hour and nobody can help, it may be better to use a completely new template that works and customize that bit by bit.
In which case, I’m using this template (the author has a demo vault as well):
And my customization based on a user’s requirement (I did not place any emphasis on changing colours there, mind you):