The components involved in histological staining are dyes and proteins. The fundamental process involved is the chemical bonding between the carboxyl groups of one and the amino groups of the other. The commonest bonds involved are ionic bonds, although there are exceptions especially in the case of nuclear staining of DNA.
The use of colour to identify individual components of tissue sections is accomplished mainly with chemical dyes, although other means are occasionally used. Dyes, however, are the largest group that we can manipulate.