A Shader Preset is simply a single material, as opposed to a Materials Preset which is multiple materials. Shader Presets can be applied to any selected material(s), regardless of name, whereas a Material Preset will only apply to materials with the same name(s).
So, for example, if you save a Materials Preset for a human figure, it will only work on another figure with those materials. That’s why I said saving a Shader Preset is better. You can apply it to any materials at all, no matter what names they have, and it will work on human figures, buildings, props, etc.
To save a preset
1. Select any prop or figure.
2. Select any material on it (in the Surfaces pane).
3. Set up the material the way you want it (white or whatever)
4. Go to the Save menu (in the content pane) and choose Shader Preset, then name it.
To apply a preset
1. Select a prop or figure.
2. Select the material(s) you want to affect. (To select more than one material, hold down CTRL and click their names)
3. Apply the Shader Preset you saved
Note that you can also choose to save a Custom Preset in the dialog. That means you could (for example), only choose to affect the Diffuse Color by making it white, but leave all the other settings unchanged. That would leave things like Bump maps in place. To do that, just choose Custom, expand the channels and only check the ones you want to affect.