Interesting subject! Not sure if this is what happened. But I’m not dismissing it entirely; Experiences has shown that eyes+brain behave weirdly at times.
The colours I was looking at are the ones I see on a daily base and these are colours abundant in nature: Green/brown bushes and shrubs, grasses in all its green variants, cornflowers, red/yellow/orange flowers etc etc. To give you a rough idea, it was very close to where I took this shot. So, all natural.
It was as if someone turned up the saturation a few notches and everything had a slight halo. It appeared and disappeared the same way a rainbow does, only the duration was shorter.