After you have found a large number of backscatter using Select Multi or Select Small, you can use the Color Mask command to easily limit the backscatter that will be processed to a particular background color.
After selecting the Color Mask command, it may take a few seconds as the software generates data needed to determine how to filter backscatter. This is especially true when the selection area is large, and hundreds of backscatter are found.
The Color Mask dialog has a Color Picker that lets you select the color of the background that you want to find backscatter on, and a Match Strength slider that varies how close the matching colors are to the picked color. The Edge Limit slider controls how much the backscatter has to be in the selected color area. Invert Mask lets you avoid areas with the selected color. The first time you use Color Mask on a photo, the Color Picker will be white and no masking done. Once you pick a color, masking is performed, and that color becomes the default for the next time the command is used. You can always pick a different color. Select OK to use the Color Mask or Cancel to deactivate it.