^I'm skeptical of the idea that psychedelics can make us perceive novel and independent environmental stimuli, such as other wavelengths of light. Our eyes and rod and cone pigments don't change because of psychedelics--and so we wouldn't suddenly have new photoreceptors sensitive to empirically detectable light types whose activation would then correspond with new color experiences.
Colorblind color grapheme synesthetes (they see particular colors around meaningful written symbols) sometimes report that the colors that appear around certain graphemes are "alien"; they are not colors that they have ever encountered in the environment. A red-green colorblind synesthete may see red around a particular grapheme even though they've never seen red at a stop sign, suggesting that certain colors do not require direct experience to be processed as unique qualia--they're born in. But, if I recall correctly, synesthetes with normal color vision sometimes also report "alien colors." They've presumably have seen all the colors the rest of us have seen but also perceive something additional. For most of us the experience of color is processed directly from the environment through our eyes, as in pulling up to a stop sign and seeing red, or as a memory, as in dreaming the sight of a stop sign.
But color grapheme synesthetes experience color in accordance with the concept of a symbol (very sensitve color-graphem synesthetes have reported that the Roman numeral "IV" has the same color aura as "4," for example. The indication is that the color experience derives from the idea rather than the physical symbol. In synesthetes, higher order conceptual processing feeds back into color perception and alters it in ways that conflict with direct environmental signals. Therefore, these synesthetes have a unique processing dynamic to their production of color experience. They are experiencing the color of a concept like "four" and integrating it into their eye-based perceptions of the various symbols for four, and new experientially distinct colors presumably emerge during this distinctly different kind of activity.
Though I have not experienced it, I don't doubt for a second that it's possible to see new colors on psychedelics. That's because I've experienced extra-spatial perception using ayahuasca and salvia together, and I'll never forget it. I briefly experienced more that three spatial dimensions, which is an experience that has been reported by a few others as the result of smoked DMT. I repeated the word "impossible" out loud to myself during and after the experience ended because it surprised me so much. We do not live in a more than three spatial dimension world (at least not that we are sensuously aware of), and the idea of "imagining" more spatial dimensions had previously seemed an absurdity. I don't believe I saw into another physically existing higher-dimensional world that night, of course. Rather, I conclude that, at least with the help of drugs, our minds are powerful enough to conjure fundamentally unique and independent qualities of experience such as new colors and additional spatial dimensionality.
