The third hit on a google search tells us that:
"A c-type print, such as Ektachrome, is a colour print in which the
print material has at least three emulsion layers of light
sensitive silver salts. Each layer is sensitised to a different
primary colour - either red, blue or green - and so records
different information about the colour make-up of the image.
During printing, chemicals are added which form dyes of the
appropriate colour in the emulsion layers. It is the most
common type of colour photograph"