I just received a Bricklink delivery with pearl gold pieces (see right-hand side in the image). This colour is less shiny and has less of the pearl effect that I used to expect so far (left-hand side, parts from an older set). Did I miss anything about a change in the colour? Or is this part of the (nowadays) normal colour variation?
Metallic plastic is always tricky, especially when dealing with acrylonitrile butadiene styrene (ABS for short). The granules (small plastic pellets) for the metallics are really sensitive to light and time, and the process can alter over time.
The stronger colors (ie. the base chromatics) are easy to get right since the granules are all from the same source and designed for that specific color. Where some of the more "exotic" colors, a mix of granules are being used, and that can be tricky.
So the process that a batch of pieces from 2018 and the same pieces molded in say 2020 might have some coloration differences, and it is a heck of a job to keep track of.
Even without direct changes in the formula, a slight change over time can happen. If this makes the pieces unwanted for you, I would reckon you can argue with Bricklink for a refund, but I would not bet that they can do much for you.