I'm really prone to fading so I've avoided using HCC right after coloring for a week. I also avoid using it as my poo immediately before coloring.
I emailed Jess about it, and she's had no color fade from HCC after coloring. I'm not sure if she's covering grays or just changing her hair color though. For me, it's the grays that fade so easily so I use the RC poo and condish after coloring, just to be safe.