Greg Spurgeon's color chart ought to be required reading for collectors. One factor that is frequently overlooked is the type of light in the area. Sun light and Florescent light may change the appearance markedly, depending on the chemical makeup of the glass. I have one piece that is light blue inside and violet outside. It is a small blown vase that I bought at Wheaton years ago. I carried it back into the shop three times before my brain accepted the fact that it really did look that different inside and out.