You know the default Photoshop UI with all of its dark interfaces? Sometimes, you might want to change that default background because it might make the colour editing easier in a way that see certains colours better. Or you might just want to change the background colour because the old colour annoys you.

To accomplish that, right-click on the background and you can change the colour to something already preset or any colour you want.

I prefer a light grey background.

Cheers,

Tristan