This principal can be used in surgery as well. Blood is red. It absorbs all the wavelengths of light except red. If the incident light is White (R + B + G), the Blue and Green are absorbed and the Red light waves are reflected. If on the other hand, the incident light is filtered so that only Green light is incident, the Green will be absorbed and the blood will reflect no color. Thus, the blood will appear black.

Principal of Color Subtraction, Refraction, Transmission, Reflection, and Hair Restoration Surgery

Typical hair restoration surgery involves use of white light as the incident source. One of the aging processes is the loss of pigmentation in the hairs. White hairs absorb no color, which results in greater difficulty in the preparation of grafts. The surrounding tissue is a combination of white and yellow structures. The adipose is yellow and the upper dermal layers are a shade of white.

When white light is shown from above, the white hair will transmit all the light, absorb no light, and have no contrast with the surrounding tissue. This makes it very difficult to see the white hair and results in a marked increase in risk to the white hair through the dissection process. The following photograph is taken of a narrow sliver hand cut under a stereoscopic microscope so that the tissue is one follicular unit or group wide. You can easily see the pigmented hair of this graft. Even with the tissue cut this thin and a 20X magnification of the tissue, the white hair is very difficult if not impossible to see. This is the best technology that most physicians have available to them. The majority of physicians do not even take advantage of this limited technology.