If you get coloured glass too hot you can 'burn out' the colours. I suspect this was overheated in the glory hole after pick-up, so the top surface was damaged. Another (slight) possibility is that the colours are sensitive to reducing / oxidising atmospheres, and the colours have been oxidised.
Thank you for confirming one of my suggestions as likely cause: overheating - which obviously would be more critical for some colours than others.
Now - at which state?
1.step: canes are laid out on heated plate. What doesn't really show up in the images: the fact that canes are all of slightly different length shows up when viewing the weight through the base. So the cane ends sitting on the plate turned grey - unlikely at this stage, as the plate wouldn't be that hot.
2.step: canes are taken up with a first gather of glass - which doesn't have any effect on the colours at this end, and even less likely at the other cane ends.
3.step: what? I always assumed that a second gather of glass would be added to the other end - or would the canes and first gather go directly into the glory hole? If my assumption (second gather) is correct, I would be surprised that this would still be too hot, after being transferred from the glory hole to the (unfinished) weight. On the other hand - if a second gather is added outside, and then the entire piece is put into the glory hole again, I would assume to see the overheating effect not on one side only.
On the ID front, I have never been convinced that there were many paperweights 'made in China with Murano canes'. There may have been some, but I suspect Murano canes were quickly copied. The canes in your weight do have a Murano air to them though. Could it be a Murano whose base was never polished because of the damage to the canes?
I am sure Murano canes have been copied in China - but these would be exceptionally good copies: they all show up in the Effetre catalogue (not sure which year my copy is), and two I actually have amongst my sample canes.
If not made in China, I see two possibilities:
1. Made in Murano and not finished - but is polishing that time consuming that a "second" would be ground flat, but not polished?
2. Made somewhere else in the world - as we know Murano canes were also used e.g. in the USA, but I have never heard about US makers copying Murano canes. Would this be more likely?
Thank you, Alan and Sue, for your comments - Wolf