I don't think there is such a thing as 'institutionalised' classism, since class in and of itself is a social institution. 'Institutionalised' in this context means that the government, or any other power that hold the reins, prevent a minority from getting equal treatment - class is a way to do this, making it one of the tools a regime uses for institutionalised discrimination.
For example the class of 'Burakumin' or undesirables in feudal Japan that has bled over even into current day Japan, or a big divide between private schools and state schools offering better or worse chances respectively at academic excellence to children (who should statistically have the same amount of intelligence on average), making it effectively so that there is a class of poorer people that cannot afford tuition, who then cannot get the diplomas to join the class of well-educated citizens.
Colorist is not a term that needs to exist, nor is it one that we should want to exist, since it waters down the issue of discrimination and racism to something that allegedly happens between different skin-colours, nullifying all the progress made for minorities not in that extremely niche branche.
All it does is isolate and divide your own cause. There is a reason feminists, people of colour, homosexuals and the working class protested together in the 60s 70s and 80s: they were all discriminated against, but not all 'coloristed' against.