Grey matter (which is only grey in preserved tissue, and is better described as pink or light brown in living tissue) contains a high proportion of cell bodies of neurons.
White matter is composed mainly of myelinated axons, and takes its color from the myelin.
Typically, each body segment has one ganglion on each side, though some ganglia are fused to form the brain and other large ganglia.
The head segment contains the brain, also known as the supraesophageal ganglion.
It controls the mouthparts, the salivary glands and certain muscles.