Colors don't work this way.
You got five colors: Red, Blue, Yellow, Black, White. Mixing them makes everything else. You cannot imagine seeing anything beyond that, as those are the only colors in the visual light spectrum.
Going beyond these colors just takes you into Inferred and Ultra Violet, which are as visible as Radio waves, Micro waves, Radiation, X-ray, etc.
The best I can do is to claim that there is another color that one can imagine that is the absence of color, not black or white, but nothing. Words fail to describe it, but when your thinking of seeing no color or nothing, this is the color your brain sees. Though for all purposes the color used for this, you'd do just as well to imagine that it is the same as Black or White, since your eyes will never see anything more colorless than that, unless you count seeing the transparent.
Technically, humans have similar limits in the ranges of sounds we can hear, and smells we can smell. Smells work similar to colors too, but there are a lot more than 3 primary smells, and since this is based on the chemical structure of particles in the air its totally possible for there to be more smells than we can smell. In fact, the general theory now is that everyone has a primary smell they can't smell, which alters how everything smells to them. (If you couldn't see blues, then blue things would look black, purple things would look red, and green things would look yellow.) And since smells are strongly connected to our memory and mate selection, the implication that everyone's smell is incorrect may explain why we differ so much.
