It is mentioned often that tru-oil ambers-up over time. Here is an example:
Kit freshly strung up in May 2015
And how it looks now, late January 2022
Note that the same colouring was used on the body and the REAR of the clear pickguard.
The body was finished with tru-oil, there's a build diary somewhere.
I know the lighting for the pics isn't the same, but the difference in colour is pretty obvious.
This is purely for illustrative purposes, make of it what you will.