To include a colored background or an image that covers the entire slide, follow the steps below.
To have greater flexibility with headings, have them in a box separate from the text.
Follow instructions to the left for adding color behind the box.
Unlike the text, you can use create a good impact with a dark background and lighter colored font.
Make sure the corner style of the colored rectangle is complementary or the same as the text box - it should have a cohesive look throughout.