In this version the game window goes red when minimizing/maximizing it. It takes just the moment but looks ugly - just a suddenly red flash.
wich operating system you use? wich of the builds are you using?
I use Windows Vista Business 32 bit. Previous Simutrans versions didn't have this bug on my machine.
SDL or Windows version? Have you tried both? Maybe it's something specific to vista? Windows 7 doesn't show that behaviour.
I use SDL library downloaded with version 112.1. I havent't tried another version.
Try the SDL version please, just to see if it makes any difference.
It turns red when you minimize/maximize while playing or when a loading bar is shown on screen?
I never minimize/maximize a window whilst game loads.