Yeah, CAC only states "
Insert has been artificially faded to achieve this hue", so not clear how, chemicals or otherwise, but retains the 'shine'.
Whilst I always tended to favour the idea you're just seeing the base ally under the gold, where it has been worn down / faded / bleached, it's still very common to see a strong blue, with the gold numbers faded to silver. The gold seems to fade far, far quicker than the main colour (see also black/gold). To me that says that the gold is a thinner layer or a dye that fades much quicker, which I guess is possible.
Not entirely convinced about this insert but, if GEN, this probably explains my point better:
https://www.ebay.co.uk/itm/254878040253
I absolutely adore this insert but... not the price (again):
https://www.ebay.co.uk/itm/305662171797
That one again, if GEN, screams artificial fade and is very reminiscent of the artificially faded CAC 5-digit "teal".
I quite like the slightly 'off' silver of the faded gold numbers as they can go nicely with pumpkin lume plots and hands.