Could what you have be like a visual migraine? Like, a rainbow aura that covers your entire field of vision, but with no headache or pain?
Visual Migraine Animation - YouTube
I get them occasionally. Mine have always been related to being exposed to quickly flashing lights, like driving past a large row of trees, where the sunlight is dappled through the leaves, and you're quickly driving past shade sun shade sun shade sun. Like that.
One data point you might find interesting: I get the visual migraines only when I'm in ketosis. I have never had one at any other time. If I increase carbs, no auras.