There's really only a couple of choices if you feel the item was described correctly - your listing states no returns are accepted, which you're well within your rights to uphold in change of mind situations, but you could accept a change of mind return if you wanted to, with original and return postage remaining the buyer's responsibility (i.e. they pay to return, and you refund the item price). 

It's difficult to say for sure if the buyer insisted on not as described, and what the result would be if the raised a return request - I know purple is one of the more difficult colours to photograph, and I also know that translucent dark purple glass seems to be a little difficult to make, as often they have a kind of red wine tone to them rather than look like a true purple, but are still described as amethyst purple, so just personally, whenever I see the words "amethyst" "purple" and "glass" in the same title, I do expect to see a bit of red. 😄  

Your images do look more reddish around the light bits, but then towards the centre it looks closer to a darker, amethyst purple. I know for certain that PayPal don't consider an item "significantly not as described" if colours are interpreted differently (the example they give on the site is "the item is aquamarine but was advertised as teal"), but I can't speak for eBay or whether or not this would count as "buyer's remorse" in their eyes.

Not much of that probably helps at this stage, though.