I've always used Wilton gel colors for red, but it is yucky for black. Turns a nasty greenish color. I use Americolor for black. Sorry.
I use Wilton ‘no taste’ red color. The other Wilton reds are bitter and you need a lot.
You can buy Americolor in the UK from Cake Stuff, The Cake Decorating Co and Cake Craft Co.
Ohh thank you so much....
Americolor tulip red gives a nice red color