Quickly set the background color for transparent pictures.

[Mapaler]

I need to modify the background color for different ID photo requirements, so I made a transparent background picture of the photo.
Now I need to open an image editing software to modify the background color.
I want to use XnViewMP to set the background color directly, then I can quickly export the specified photo size.

[xnview]

you can use 'change color depth'

[Mapaler]

you can use 'change color depth'

I know how to use it, thanks.