Alrighty, I did some testing on a piece of paper, including some highlighting with a purer red, but I think that the solution I came up with is the best compromise between speed and desired look. I highlighted with Vallejo's Bright Bronze mixed with some GW Mithril Silver, drybrushing the rough bits and normal highlighting the smooth bits. I then airbrushed blood red heavily thinned with water, and after that a layer of black ink mixed with a little bit of red shade, also thinned with water.
It's not entire the effect that I first envisioned but I'm ,liking it nonetheless. The deep red copper tint looks more muted than a pure red, and the reddish hue on the black armour gives it a look of dark, dried blood. Which is appropriate for, well, 'Blood' Angels. And I'm also quite confident that once the other detail colours are on that it will tie the unit in decently with the look of the rest of the army. The brass/bronze, some green, the parchments, some metal detailing. There's even one Marine that has a loincloth that I will do in that khaki colour.
What say you?