I've hacked together a solution that seems to work for me, but I'm sure I've missed some intricacies and so don't want to PR yet. I'd like to request changing Plater.SetNameplateColor (unitFrame, r, g, b) to Plater.SetNameplateColor (unitFrame, r, g, b, a), and similarly for any other API functions that allow for setting colors. This would involve updating Plater.ChangeHealthBarColor_Internal and probably a number of other functions in a small way. I don't think it would break the API for any existing mods, but I think it's a valuable feature to have.

Let's see the PR :)

Done. #78