I have a thing about blue food!
I've known about the beautiful colours produced when one combines egg yolk and red cabbage for years, but am only now starting to experiment.
Here is the first fruit of my labours: an omelette made with fried, shredded red cabbage.
I think I may be able to get more intense colouration by leaving the mixture to stand for a while before cooking. It was also somewhat overdone - better over cooked than under cooked as a general rule.