I don't know... I would still hold to my original speculation that the paint would overwhelm the color particles and alter or block the particles ability to refract/reflect light.
I understand what you mean about the roll on paint being extremely thin with each layer that we apply. That does make it a 'little more' possible then if it was just straight paint ( without the heavy thinning that we put it through )
And I can also see how a build up of multiple layers of our thin mixture 'might' give give some effect... ( here we are dealing with how light would reflect/refract off the multiple depths of the paint with those color particles in them.
But I suspect that even our thinned paint mix would lay on 'some' color coating that would greatly reduce the effect that those color particles can give.
In the case of a multi-layer paint job with the particles, I would suspect that the accumulative layering of colored paint would basically 'tint' away the full color spectrum that those particles are designed to give. For example, if you used them in a multi-layers baby blue paint... the particles would tend to take on a baby blue effect and lose the other colors of the spectrum.
The best place for the optimum effect of those color particles is on the final layer only. Because you have to just imagine how they work... they need the light spectrum to be able to reach them, in order for them to refract/reflect the color spectrum back at you.
Anything that affects the amount of light that reaches those particles will in turn reduce the amount of reflection/refraction that they give off.
That is why a 'clear coat' applied as the final layer... is the most optimal situation to allow the particles to do what they are designed to do... refract/reflect colors of the light spectrum.
Maybe someone will invest a few bucks and give it a 'real world test' to see if my understanding of light refraction/reflection proves correct or wrong in actual practice
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