added two sentences to the Idea-section, to provide more of an explanation:
If the gauge group is SU(N) and fermions are in the fundamental representation of dimension , so that has a linear basis of elements, one says that these are colors of the given fermion particle.
Hence, more generally one could reasonably say that the “number of colors” of a given fundamental particle in gauge theory is physics synonym for the choice of linear representation of the gauge group that defines this particle.
stub entry, for the moment just so as to satisfy links
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