All of the 2015's that I have worked on do not have a diffuser paper on the back of the meter . Just change the light and see if there is a difference . I personally like to use warm white LED's when replacing the lights (lamps) . Some times the old incandescent fuse lamp will get dark on one end. There might be a burn mark or smoke residue on the back of the meter . Just some ideas .
I believe the plastic back of the meter housing is blue, lending that color. I have not opened a 2015, so they may not have velum behind the meters. But the larger 22xx series does have velum paper diffuser behind the meters. I have replaced several of them and the meter color returned to its original color without the yellow or brown tint.
There is a pair on the auction site now if it comes down to it. Loosen the two screws on the lamp bracket, pull out of housing, and you should get a good view of the back of the meters.
Yes you did ...
https://www.ebay.com/itm/Marantz-22...079693?hash=item441363bd0d:g:OUYAAOSw~XpZUB-k
https://www.ebay.com/itm/Marantz-22...221076?hash=item467287ebd4:g:TKwAAOSwrfVZUB9u
Do a search on "Marantz 2245" and you will find lots of parts.
Good Luck!!!
The meter in the photo does appear to have a browned velum. The brownish paper surrounding the blue back of the meter is the velum. It covers most of the back, which is the same color blue as the part you can see. I’ll bet the meter is fine and you just need a new velum.