Replacing kitchen light, house wiring to box: 2 white twisted together (neutral), 1 red (hot when switch is on), no ground. Fixture: 1 D shaped ridged wire, 1 smooth (round) wire, 1 ground wire. My guess on connections, D shaped fixture wire to white house wires, smooth (round) fixture wire to red house wire, fixture ground wire to metal fixture box? Is this right?
When a light fixture has two wires of the same color it usually means that polarity isn't important. However, the ridges/ribs may indicate a neutral. Go with your plan.