albedo

The fraction of incident light or radiation reflected by a surface or body, commonly expressed as a percentage.

For track, painting rails white at weak points that are more prone to buckling (where the 'critical rail temperature' is close to the 'stress free temperature' [...]) increases their albedo and can help slow how quickly they heat up, reducing their temperature by perhaps five degrees or so.

The whitish inner portion of the rind of citrus fruits that is a source of pectin, commonly referred to as the pith.

One of the four major stages of the magnum opus, involving purification of the prima materia.