The vast majority of multiple sclerosis lesions occur in the white matter areas but a small number, about 5%, do occur within the grey matter.

The grey matter is so-called because in section it has a grey colour due to all the grey nuclei in the cells that make it up. In fact, in the living body, grey matter is pink.

The neurons in the grey matter consist of neuronal cell bodies and their dendrites, the short protrusions that communicate with immediately neighbouring neurons in the CNS. In contrast with the neurons of the white matter, grey matter neurons do not contain long axons that transmit the nerve impulses to more distant regions of the CNS.

About 40% of the human brain is made up of gray matter whereas 60% is white matter. However the gray matter consumes about 94% of the total oxygen used by the brain.

Grey Matter Links:
Grey Matter Technology - The Brain
ScienceNet - What is the difference between white matter and grey matter?
Brain Salad
NeuroNames Brain Hierarchy
Brain Facts and Figures 

MS Glossary
All About Multiple Sclerosis