Maroon - deep reddish/brown, I guess. I would suggest Harbor Freight, Lowes or other hardware stores.
The Grey ScotchBrite is finer, but the maroon has worked well for us now, on a few barrels that were harmed by using boiling hot water for cleaning.
Hint- cold water actually cleans better and doesn't "glaze" the fouling, but dissolves it.(hint from Holland and Holland, themselves - their word re: glazing the fouling)