Could it possibly be the mutated variety of Dendrobium Liberty? I think I see green striping on the petals. I've never seen a Liberty with a purple lip, but then all the ones that are just green and white seem to have "White" included in the name somewhere, so there could perhaps be a version out there that exhibits the mutation but retains the purple in the lip. Do a Google search for Dendrobium Liberty Mutation and you'll see lots of pics. Perhaps one will look like your mystery orchid! Beautiful, by the way!