I recently used a bit of black roast barley to color a bock. I didn't want any of the roasty flavor, so instead of adding it to the mash, I cold-steeped it in a cup or two of water for 24 hours, boiled it, and added it to the fermentor. I tasted the extract before boiling and it was pitch black without much in the way of coffee/roast tones.
I think I used 1.5 ounces. Not sure there was any risk of picking up undesired flavors, but this made me feel better about myself.