Here is a wordy but interesting mechanic I made for a B/R Dwarf faction. The Ghurzad are greedy and reckless in their neverending search for gold.
Dig [Number] (Exile the top [Number] cards of your library, then put a colorless Gold artifact token onto the battlefield for each land card exiled this way. They have “Sacrifice this artifact: Add one mana of any color to your mana pool.”)
It’s red because it’s reckless, and it’s black because it’s greedy. Giving up cards in exchange for ramp/artifacts is clearly B/R to me.