I have got differently in colouring my butter cream icing. I cannot make red , pink colour properly. I am using foster Clark food colors
I am not familiar with the Clark food colors that you mention, but for pink- it only takes a tiny bit to make a soft pink.
As for red: I always recommend tinting the icing with pink first, then use your red color to get it to the shade you want. And remember, the longer it sits, the darker it becomes. And generally, it takes a LOT of red to get the right shade!