Keynote is a presentation software program made by Apple and sold as part of Apple's iWork software bundle. Making presentations that can be projected onto a screen is an effective way to provide a visual with key information for your audience. Keynote allows you to use premade theme backgrounds, or you can fill the background with a colour or image.
Open Keynote and the presentation you want to edit.
Click "Themes" on the toolbar. Select any background theme to change the background throughout your presentation.
Click "Inspector" on your toolbar, and then click "Appearance." Choose "Color Fill" to fill your background with one colour; "Gradient Fill" to have a fading colour background; or "Image Fill" or "Tinted Image Fill" to set an image as your background. Click "Choose" to select an image from a file on your computer.