I've had a rainbow experience a couple of times - I believe it's a sort of migraine tho' there was no pain with it. Just a slightly odd feeling and I had to sit down for awhile.
I became aware of a sparkling effect in one eye and it was like a slightly blurry patch from the centre down to the bottom but the outside edge was clearly zigzag and with the rainbows - like angular prisms all around the outside. It slowly grew but then gradually it started fading until after about 20 - 30 minutes it had gone.
I'm normally long sighted and have always had good eye sight but my poor old eyes are losing the ability to focus on small print, but that's just my age.
Robyn