Hello Neal MA. to remove colors with PhotoPad, you can use the color removal tool. You can open PhotoPad, load the image you wish to edit, click on Tools > Color Removal and select the color or use the Eyedropper button and clicking directly on the image to select the color to be removed.
For more details, you may access the user's guide by clicking on the help icon located at the upper right-hand corner of the program's window (Questions Mark Icon for Windows and Lifesaver for Mac).