I have pretty extensive experience with a range of nootropics, racetams included, and in my opinion the HD vision and colour brightening effects are somewhat overstated by people who are into these things. If someone takes a racetam and actually manages to read an extra line on a snellen chart or scores higher on some kind of objective colour-perception test, I'll be convinced, but until then I think this kind of "the world just looks brighter!" type effect is largely placebo and/or a perceptual side effect from the slight mood boost after taking what is, essentially, an unusual stimulant.
All that said, Coluracetam unlike the other racetams I believe has shown some beneficial effects on optic nerve injury so if any racetam did have some objective effect on vision, this would be the one.
Unfortunately I can't comment on the combination of coluracetam and a psychedelic, not because I haven't had the opportunity exactly, it's just something I haven't yet got round to doing... I have however combined nootropics with both stimulants and downers, and generally found they really smooth out any stimulant induced anxiety and even dampen physically negative effects, as well as work to add a layer of lucidity and block amnesiac effects of many downers. By most reports all racetam nootropics potentiate all psychedelics, sometimes massively, so I would suggest caution and taking as little as half the dose of a psychedelic you would usually take the first time you combine it with a nootropic.
I have combined noopept (which although not a racetam I believe is somewhat similar in action) with 4-AcO-DMT twice and both times I ended up aborting with benzos, however both times I was a little drunk and made a stupid decision that it would be fun to trip spontaneously. I do plan to one day do this starting from sober like would be sensible, and ride it out, but from my brief experience both times the comeup was very very intense, followed by hugely potentiated hallucinations that just covered my field of vision. For me the hallucinations were a little different in character also, I'm not sure how to describe this but if you are familiar with the sort of "zooming" inwards and outwards type effect that is maybe more characteristic of LSD than shrooms, it was like this, but applied to the whole world, like the air was thick with hallucinatory cobwebs... there are also a bunch of stories on the internet of people taking noopept and shrooms and having terrifying experiences.
Noopept is a strange substance though, so on topic, I would suspect Coluracetam would not be quite the same as this although there would still be potentiation. It is also fairly short acting (around 4 hours or less) so if you take a long acting psychedelic it's possible there would be a perceptible miniture comedown halfway through where things get a little more normal (relatively speaking)... this is purely hypothetical though.
