The background is the background pattern of each slide
The "master" is a special kind of slide that contains placeholders for slide text and footers (such as the date, time, and slide number) that control layout elements such as the slide's fonts, font sizes, colors (including background colors), shadows, and bulleted styles. including background color), shadows and bulleted styles and other layout elements. Masters usually include slide masters, title masters, handout masters, notes masters in four forms.
The color scheme allows you to customize the colors on the various masters that come with it.