Originally Posted by lumpher
if you just want the color, drop in 1/2 lb of dark brown sugar into the porter
Um... I'd avoid that. It'll increase the alcohol, thin out the body, and not contribute that much color. Instead, I'd go to your local homebrew store and get some dehusked carafa special III. Grind it super fine in a coffee grinder and then cold steep in cold water. Filter out the grains, boil to sanitize the mix, cool, and add to your fermenter. This will add significant color without contributing to the flavor too much.