WallPaper

You can change the colors tn the color themes:

Menu / Desk Light Color Themes / Edit: Write in the UI Color Filter (in the right titlebar): "Desklock"

Note: if you change the color directly, it will also be changed in the "Color Definition".

I prefer to remove the reference in the "ColorDEfRef" column

Or you assign an appearance with an image to your user. The image of the appearance will be used for the desk lock.