I've used this as an example of (non)-vector spaces in a linear algebra class before. Light perception is based off the stimulation of three color cones, so thr

I've used this as an example of (non)-vector spaces in a linear algebra class before. Light perception is based off the stimulation of three color cones, so three (positive) values. The light available to us stimulates those cones in certain ways and three light colors are enough to form a "basis" of the space of perceived colors. But the fact that the values are always non-negative means that there are possible cone-stimulation values that are never achievable by our light. However, super-saturating your eyes with a color and then removing the stimulus effectively allows you to also "subtract" out some light and therefore reach parts of the perceivable-color-spectrum otherwise unobtainable. I thought it was a clever application but my students didn't seem too impressed!