I think most of the nice/pleasant colours are given to lower rated participants consider the following

Grey — boring colour

Green — usually associated with positive events

Cyan — pleasant colour liked by everyone

Blue — decent colour somewhat exciting due to association with unclicked links

Purple — disappointing colour due to association with clicked links

Yellow — annoying colour due to pretentious people calling yellow traffic lights amber

Red — usually associated with danger

Nutella — not a colour adding to bread yields significant improvements to taste