I've introduced the color to Ollie in a number of ways and first attributed his not liking deep blue things to the item - but they add up. For instance, I gave him a little clear glass bottle with a cork in it. He loves it and sleeps holding it. Then I tried to give him a similar bottle that was dark blue - he wouldn't take it. The same thing happened with a dark blue bioball. We've frightened him wearing dark blue clothing. I don't really want to continue the experiments, because they make him unhappy.
Ollie sees things outside the tank and reacts to them. I've started experimenting with colors that I wear when playing with him. Today I wore purple, and Ollie turned from orange to the very same shade of purple I was wearing (not his usual shade).
There were reports last year from a vulgaris owner that his vulgaris had an aversion to yellow!