But, alas, this color space has some unhelpful properties. For one, not all triplet values (also called tristimulus values) are physically possible. Consider the LMS coordinates (0, 1, 0). To physically achieve this coordinate, we would need to find some way of stimulating the M cones without stimulating the L or S cones at all. Because the M cone’s sensitivity curve significantly overlaps at least one of L or S at all wavelengths, this is impossible!

Impossible color!