I could easily be enlightened otherwise, but I'm not sure the Tru-Color "primer" is a true primer. I have it, but in use it is no different than their other paints in (apparent) tack or tooth, or anything else you would expect of a primer. I think is just a primer color - a dark one at that - and not something to condition a surface for other finishes. The primer color is so dark it can't be used alone under reds or yellows; I had to use their white to prepare for these transparent colors.
As to brass, I don't know firsthand, but a brass project is on my short list. Let us know how you fare if you try it.