In ~2016 on the chan someone posted a completely unhinged post about this "bleen" "grue" color that nobody could see. it's probably lost to the ages now, but I remember it.
i still kinda do, because it just happen at random when i am outside. sometimes, usually in bright morning light, sunny morning. no i dont look at the sun, yes mostly its visible looking at the blue of the sky.
last time i had it while in 1 on 1 with my manager. it took a lot of struggle not to try and rub my eye or tell her i was seeing this weird rainbow snake floating around.
overloaded cones, hopefully thats not some indication of something bad but just 'tired eyes'.
Sounds like it might have been a 'floater':
https://en.wikipedia.org/wiki/Floater
(I've had one myself for my whole life, a 'crystal worm'. I usually don't notice it, fortunately, but once it a while it will noticeably drift into my field of view while looking at a bright, blank field - like the blue sky or a monochrome computer screen.)