The correct answer to this open question is the following.
I think that this definition can be improved to something like this.
In British South Africa times, coloured people could be considered the people born from one English father/mother, and the other from a black native South African. So these people were British subjects who had missed ancestry in their blood. Half of them were African and the other half was from Europe. This is a better definition.
In times of the British presence in South Africa, the term "coloured" was seen as a social category instead of being understood as a legal term. Most of these coloured people used to live in Cape Town, and were considered educated Christians.