Coloured as a designation was one that flattened the distinct histories and bloodlines of a number of mixed race groups.
Cape Malays, Griquas, the Cape Coloured, along with eastern South African mixed populations were all put under the collective "Coloured" in the Population Registration Act of 1950.
The formation of a mixed race identity arose from the "free black" population of the Dutch colonial era.
They formed the foundations of multiple groups (one such being the Oorlams that sprand the Griqua and Baster folks) being made up of emancipated African, Asian and Mixed people who assimilated into a westernized Dutch and Dutch Creole speaking community.
However mixed race ancestry in an of itself is not the foundations of Cape Coloured, Cape Malay or Griqua identity.
For example the abeLungu were known as a Xhosa clan with several european forebearers and retained phenotypical traits and yet they were never anything but Blacks legally and socially.
Mixed Race status was alotted in the colonial era to those of mixed race ancestry in the colonies who approximated European folkways.
I'm not sure what point you're trying to make.
People of different ethnic backgrounds and traditions were all counted as white - British, Afrikaans, Portuguese, Greek, Jews etc. And ditto with black people - Zulu, Xhosa, Sotho, Pedi etc. were all counted as black even though there were many differences in language, culture, and so on.