Is there a difference between violet and indigo?

That depends on whether or not you're talking about the colors themselves or if you're talking about the Energy differences from the chemistry equations for R.O.Y.G.B.I.V. In case you don't know what that is that would be the atomic spectrum's. RED, ORANGE, YELLOW, GREEN, BLUE, INDIGO, AND VIOLET. So in all do respect there is a difference between violet and indigo, violet is purple and indigo is a dark blue. Besides Violet and Indigo have two completely different nanometers.