After an update I noticed discover was this weird yellow color, I opened settings and noticed it too was yellow, thinking it was some bug, I restarted PC, now everything is yellow. I tried inverting colors but that is something completely different. I'm not even sure what was updated to cause this.
New plasma update sets the accent colour from your background. To change it go to System Settings > Colours and Themes > Colours (not sure if Mint has it in the same place) then set the accent colour you like from the top.
Oh I see, that is odd. I thought your background was yellow beforehand. Is it perhaps plasma's Night Light? That will tint everything yellow when it's enabled.