I actually thought of this a couple of days ago. I'm so glad someone requested it!Why Hidden?
I think they all should get their each separate colour. Hidden and no mod should stay the same though.
Anyway, I actually support the Idea of a own colour for HR and DT. There's actually no need for more colours as silver, gold and a third one.
Maybe a 4th colour when you have something like HR+HD or FL+HR+DT, etc.