would love to use black more, but has a funky aftertaste. red too, but i've found the wilton's no taste red. i'm going to be ordering some Americolor black to use on my next project (can't find anything but wilton brand at the local stores) and didn't know if a change in brands would help.
I find that the Americolor reds & blacks require much less to get good color so that there is little, or no, taste change.
For red, it's best to start with a strong pink and then add the red.
For black, if starting with chocolate icing is an option, that's the best. If not, starting with dark brown and then add black.