Because colour is not an absolute, it is a sensation in the human brain created by the colour-sensing comes in the retina. So, by this definition, if it cannot be detected by the eye it is not a colour. read more
Our eyes can only detect colors of light that we see as a rainbow, primarily shades of red, orange, yellow, green, blue, indigo, and violet. These are the specific wavelengths of light that the receptors in our eyes are tuned to. read more