I have some PNG images which consist of a black shape and a transparent background. Unfortunately, IrfanView shows transparent background as black color, so I see just black on black. I've found in Irfan settings that I can change the window's background color, but it changes only around the image, the transparent color is still black.
Is there any way to change the color displayed as transparent, or, optimally, use white-grey squares like Photoshop?
You were on the right track. IrfanView sets the background for transparency the same as the viewing color around the image.
You just need to re-open (Shift+R) the image with IrfanView after changing the view color to white.
To change the viewing color in Irfanview go to:
Options > Properties/Settings > Viewing > Main window color