I am reading about group theory in particle physics and I'm slightly confused about the word "representation". Namely, it is sometimes said that the three lightest quarks form a representation of SU(3), or that the three colors do. But at the same time, it is said that a group can be represented by a set of matrices, which operate on vectors that encode the flavor or color state. I think it's the operators (ie matrices) that are the representation of a group, not the vectors that get operated on. How can both be a representation of a group when they're different things: operator vs the object that gets operated on?