The themes that come with Keynote are sets of master slides with predefined layouts, backgrounds, charts, tables, and text attributes. You can modify these attributes to create your own masters and themes. When you change a master slide, the changes appear on every slide in the document that’s based on that master.
You can create a new theme by:
Modifying master slides and saving the document as a new theme.
Deleting all master slides except the blank one, creating a collection of master slides from scratch, and then saving the document as a new theme.
You can customize the following master slide attributes:
Default position of title and body text
Background graphics
Default fonts
Default bullet styles
Default position for objects (object placeholders)
Object fills and line styles for objects
Chart style
Slide transition style
Alignment guide positions
For detailed instructions, see the following topics: