On Windows 7 try to uncheck "Use visual styles on windows and buttons" option: Right Click "My Computer" | Properties | Advanced tab | Performance | Settings button | Visual Effects tab.

On Windows 10 ensure you have installed video card driver from hardware vendor not from Microsoft.

Windows 7 is not a Light Illusion supported OS.
We only guarantee operation on OS versions that are directly supported by Microsoft, and have not been depreciated.
Support for Windows 7 by Microsoft ended January, 2020.

Steve

I know, but fortunately with unchecked "Use visual styles on windows and buttons" Colourspace works flawlessly on Windows 7 and gives the same results as on Windows 10

Glad you've found a workaround to whatever the problem is on that PC. I too am currently using Win7 (I fully realise it's not officially supported) for various reasons I won't go into here. As soon as I'm able to move to a new PC, I will, not least because 1366x768 feels cramped! Anyway - I don't personally need to untick the visual styles button, just for information - it works as expected. HTH.