hmm. grammatically "das hier ist" isn't a typical construction in german. the verb is always the second element in a sentence. so if "das hier" is the first element, it's still weird. "it here is black red gold." are you sure it's not dass?
either way, let's say it's idiomatic for "this thing here', i would probably translate that sentence "this here is black, red, and gold--firm and proud." hart in this context is more like "stalwart" or some old-timey pre-technological revolution Teutonic militarism. and "stolz" within a metaphor about the colors of the flag has connotations like "stately", you're proud in a nationalistic, stately, superpsyched-about-your-germanness way. stolzieren means to swagger, like in hip-hop. they were looking for the rhyming couplet, mostly, also a common hip hop strategy.
ok enough of that
