The yellowish color is due to lipid in the sebaceous glands. Often more macular initially, but it becomes more verrucous at puberty because the sebaceous glands in the lesion are stimulated to become larger by hormones. There are many sebaceous and apocrine glands in the dermis.
Sebaceous cells look like foamy soap suds with a central nucleus.
Apocrine glands have a widely-dilated duct lined by two layers of cuboidal cells.