Some colours could certainly be harder to remove than others, but I posted an experiment a while back where I coloured white swatches of hair black using Majirel, Koleston and Live XXL. When I used effasor to remove them, the XXL lifted much quicker than the other two, but the condition seemed to feel the worst by far, and ultimately the strength of the hair determines how far we can process it.
I also think it has a lot to do with the fact that it is a consumer product and seeing as the shades tend to be either really deep like blue blacks or really vibrant reds I think a lot of users take the colour though every time, so many times when a client comes to us with it on their hair they have a deep build up of it on their hair.