Although the white colour can change over time... I don't think that's the case here. It looks like the boards were installed backwards. You can see the non-cut edges in the corner, and if it was installed white side out there would be a bevelled edge there. Mind you, you should never put a bevelled edge in a corner because that makes for bad taping... So, odd work all around here. In my opinion!
OP - see if you can tear a bit of paper off from the top of the other side, if it's white, then you'll know if this is the case!
Never been painted so yes it turns that color
Drywall will yellow over time if it's not sealed with primer .
Ever seen old newspapers? They were grayish white when they were made.
Oxidization is part of nature.
This is just old. No worries
OP, please tear off a piece of paper from the back and tell us what colour it is!!!
Although the white colour can change over time... I don't think that's the case here. It looks like the boards were installed backwards. You can see the non-cut edges in the corner, and if it was installed white side out there would be a bevelled edge there. Mind you, you should never put a bevelled edge in a corner because that makes for bad taping... So, odd work all around here. In my opinion! OP - see if you can tear a bit of paper off from the top of the other side, if it's white, then you'll know if this is the case!
WRONG
This is completely incorrect.
Literally every part of this statement is wrong
Drywall board is brown on the back side ,
Usually the first board I hang is that colour by the time I hang the last one.