Why does the colour wheel wrap around? Red colour bares 430-480THz and Violet bares 670-750THz according to Wikipedia.
What frequencies are the colours between red and violet? Will they be higher than red? or lower than violet?
What physically properties do opposite colours carry? Cyan is the opposite colour of red; yellow is the opposite colour of blue; green is the opposite colour of magenta. Can it be expressed mathematically?
 A: The colors "wrap around" solely due to the way human eyes perceive color.  Magenta, for instance, is actually both of red and blue wavelengths together that our eyes perceive as "a" color.  If you look at magenta light through a spectrometer, however, you'll see that it's actually composed of two different wavelengths and therefore it has no single wavelength.  It could probably be best expressed using a mathematical model of the receptors of the eye, such as described in this paper titled "A photon accurate model for the human eye" by Micheal Deering.
A: 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.[18]

Single frequencies display color, but a color corresponds to many frequencies in combination with the response of the eye.
