Greenscreen with gradient color mask
In Adobe Premiere, and other professional level video editors, it is possible to specify a tolerance for the color that you would like to remove with the chroma key operation. Apple Photo Booth allows you to take a picture and then use that matte to create transparency behind the subject, but you probably won't find this functionality in a basic editor such as videopad. It is possible to do what you're trying to do in Premiere, After Effects, Davinci Resolve, Lightworks, AVID, Final Cut X, and other video editing applications that support layered effects.