The white matter of the external capsule contains fibers known as corticocortical association fibers. These fibers are responsible for connecting one cortex, or the outermost layer, of the brain to another. The capsule itself appears as a thin white sheet of white matter.
The central nervous system is comprised of two major components, white matter and grey matter. The white matter making up the external capsule consists primarily of lipid, or fatty, tissue. White matter is actually a pinkish color in its natural state. When preserved in formaldehyde for research purposes, the color appears white. The white matter portion of the brain continues to develop throughout a person's life, not reaching its peak until around middle age.