I really do not understand why you would think that the colors would scintillate.

Image a single point source of pure red light coming to our eyes from an otherwise completely black vista. (Think:a laser sight aimed at us in a dark room.) As we move our eyes, (or they twitch with our pulse), the photons from that (for arguments sake impossibly fine), point source would alternately fall on "red" cones, "green" cones and "blue" cones.

As we move our eyeballs, the image in our brains doesn't move. The brain maps the tristimulus values originating from different (and widely spaced) cones, back to the same point within our mental image. Without persistence of vision, our perception of the colour of that single point in our mental image, would change as the photons originating from it stimulated different cones with their differing spectral responses. But that doesn't happen.

With persistence of vision, the colour we perceive coming from that point source is an averaged combination of the responses generated by the photons falling on lots of different (and different 'coloured') cones over time as our eyes move. In this artificially simple case, the colour we perceive in our brain at the point source, is an amalgam of the tristimulus responses from all the cones that those pure "red" photons hit as our eyes move, and we attach the label "red" to that amalgam.

In the real world there are no pure frequency point sources. The photons reaching our eyes from any given point (or rather, from the same directional vector), will be a mixture of many frequencies. In the case of a rainbow, given the distance between our eye and the raindrops that are responsible for the rainbow, we will be unable to resolve anything less than (say) a square foot, or a square metre, or maybe larger in the XY planes. And indeed, we mustn't forget that the raindrops that form the appropriate angle between our eyes and the Sun will not all be exactly in the same plane in the Z axis. And the raindrops themselves are falling at some rate.

So the light reaching our eye and being resolved to a single point in our mental image within any given period of persistence, will have come from some or all of the raindrops that passed through a cube (or sphere) of air 10s or 100s of miles away. And there will be some light being reflected from the outsides of raindrops both further away and closer to us that will arrive at our eyes coincident with the refracted light. And some of the spectral components refracted will have been attenuated by the air and water molecules between the refracting raindrop and our eye.

The colour we perceive will be the result of the amalgamation of all those stimulations within the period of persistence.

The important point is that I really don't understand why you think we should anywhere perceive pink in the rainbow. Particularly since I don't see it when I look at the rainbow.

Well, the first question to ask, is when was the last time you actually looked at a real rainbow with your own eyes?

As opposed to a instantaneous frozen image of one interpolated through a CCD device with some number of bits of A/D conversion, thence further manipulated (reduced) into a jpg, png or (if you are lucky) tiff format file, and probably resized with the additional quantizing that entails.

And even when you have viewed a real rainbow in real time, if one (or a dozen, or a hundred thousand) raindrops within the auspices of those nominally refracting the blue end of the spectrum, happened to have dissolved in it some contaminant that caused it to refract or reflect only the red components of the spectrum, do you think that given the persistence of your vision, you would detect the resultant, brief pink hue?

Even via the analogue processes of film or slide production, and with the fastest shutter speed possible, the energies of many millions of photons will have contributed to, and been averaged to produce the hue displayed for any given point in the picture.

All the scientific models are based around infinitesimal points and pure frequency sources, but it is naive to believe that this could ever occur outside of laboratory conditions. That's why NASA go to such great lengths to try and adjust the raw data produced by their cameras on Mars, or Cassini, to produce "naturalistic" color photos. So that we might get something of an impression looking at those photos of what we would actually see were we standing where their cameras are mounted.

The colours we perceive, and the labels we attach to them, are entirely constructed within our brains. And for any hue we perceive, there are almost infinite number of mixes of frequencies of photons that will reach our eyes in a given period of time, from a given vector, that will result in us perceiving that hue.