I use an ounce of roasted barley for color only. ~500L I believe, but next time I might only throw it in at the sparge for color - I noticed a bit of roasty flavor this time 'round.
I may even skip it altogether. I pull a gallon or so of the first runnings and boil it down to get some kettle carmelization. That gives some color, although I could care less about the color as long as the flavor is there.