I think you can set it at the DRC rule level, per the 2018.4 manual. There is a rule check comment parameter, RVE Highlight Color: color, and it is supposed to be supported for Virtuoso.
Here is a link to the manual on Mentor Support Center:
(If that doesn't take you to the page, in the manual search (search box below the blue nav bar search), put in "color" and it should be the first hit.)
Hope that helps.