Creating ICO file from white PNG files.

I took my PNG files which had black linework and used Colors | Invert to make them white. Then, I exported them to new PNG files. Finally I merged all the white PNG files into an ICO file but it shows the other images as black. Why?

I am simply trying to make a new ICO of my PNG files with white instead of black, so I can used it with Windows in Dark Mode.

See attached image.

If I change the palettes to 32bpp then they show as white.