When a sample is freshly cut, it usually slightly pink in appearance (for both types). When preserved in formaldehyde, white matter appears to be almost white. White matter consists mostly of myelinated axons:. Myelin is a lipid tissue (a fat) with capillaries. It helps to keep the electrical in the nerve fibre. This is important for fast and accurate sending of signals. In the brain white matter is surrounded by grey matter most of the time. In the spine, white matter is outside, and grey matter inside: the myelin sourrounds the nerve cells, and helps the transmission of nerve signals.