Well, "range" was not the correct term. What I meant is that you can't treat the source as sparse. You can't skip portions of it. So you can't make an array that only covers every other element of this enumeration:

  type Colors is (Red, Green, Blue, Black, Gray, White);

It has to be a consecutive group of them, taken in order, as the specification of even this enumeration has an ordering to it as far as Ada is concerned. So I can make an array using all of Colors as the index, or some subset but it has to be, say, Red..Blue and not Red|Blue skipping over Green.