It’s the theory of colour charge essentially, counterpart to electrodynamics. Quarks have colour, rather than electrical charge. Mediating particle is the gluon, analogous to (but entirely different from) the photon
Its called chromodynamics because the interactions are described by the special unitary group of degree 3, which is the same group that describes how we perceive color interactions.
Now explain how quarks have flavour!
It's just the three dimensional nature of it plus the usual physics practice of giving things cheeky names. The vector space of (visible) colors is not acted symmetrically upon by SU(3); it doesn't transform symmetrically under charge-preserving unitary matrices. A blue strawberry with red leaves would not seem the same to us as a red strawberry with green leaves.