Hi,
Kindly not that Black and White are prohibited values for WindowColor.
The specified WindowColor should have a luminosity range of 25% to 75% when converted to Hue, Saturation, and Luminosity (HSL) values. Any color outside a luminosity value of 25% to 75% is changed by Windows. If you pick white, for instance, you will get light grey.
Thus if you would like to customize the color, it is recommended that you use a tool that supports HSL to select your color and adjust the luminosity to be within a 25% to 75% range before you convert it to RGB to specify the WindowColor.
Reference link:
https://learn.microsoft.com/en-us/windows-hardware/customize/desktop/unattend/microsoft-windows-shell-setup-themes-windowcolor#values
Thanks,
Jenny