Earlier quoted context omitted.
I don't follow. Two given colors being indistinguishable doesn't imply that any two colors are indistinguishable.
Your suggestion was that if two colors are indistinguishable, they should have that name. But given any two colors A and B you can construct a sequence C1 = A, C2, C3, ..., Cn = B where adjacent colors Ci and Ci+1 are indistinguishable from each other, and so need the same name, for 1 <= i < n. Hence, A and B have to have the same name.
Think about it with numbers: if your sequence A, B, C... are each zero units apart, then yes, A = B = C = ...
In actuality, though, they are not zero units apart. They are a small, but positive distance apart. Those tiny differences add up so the distance from A to C is twice as far as the distance from A to B.