Color is a sense perception of light, dependent on the cells of the retina of our eyes.
Light is an electromagnetic wave which can be of single frequency or a mixture of very many frequencies:
This is the electromagnetic spectrum , and the part of it that is visible when a single frequency hits our eye give the color as we perceive it.
Color perception from a mixture of electromagnetic frequencies is another story. One can make full color photographs just using two frequencies, and three can give the whole palette of painters.
This image (when viewed in full size, 1000 pixels wide) contains 1 million pixels, each of a different color. The human eye can distinguish about 10 million different colors.
Single frequencies display color, but a color corresponds to many frequencies in combination with the response of the eye.