Is there any chromatic analogue of the Shepard tone?
One similar idea is the Blue Diamonds Optical Illusion, is a series of identical things
that appear to be a series of darker and darker and darker things, indefinitely.
It shows that the Cornsweet illusion can be repeated over and over again.
This reminds me of the way the Shepard tone plays the same thing over and over again,
but the pitch seems to get higher and higher.

I suspect a similar approach might be able to construct an illusion that appears to be "always getting bluer".