From Biology Forums Dictionary
Grey matter (or gray matter) is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astroglia and oligodendrocytes) and capillaries. Grey matter contains neural cell bodies, in contrast to white matter, which does not and mostly contains myelinated axon tracts. The color difference arises mainly from the whiteness of myelin. In living tissue, grey matter actually has a grey-brown color, which comes from capillary blood vessels and neuronal cell bodies.