An interesting site indeed John, and yes in answer to your question, I would always resort to fluorescent light , if only just to reassure the neodymium content.
No intention to hijack your thread Paul, but:
Interestingly, the final sentence where it says: 'and again some variation within the main colours, probably due to the colourings being hand mixed.' may have given us the definitive answer to Emmi's Wedgwood Dolphin appearing a little darker than some other Topaz pieces.