Use multiple themes in one presentation
When you want your presentation to have more than one set of colors, fonts, and effects (like shadows, reflections, glows, and more), add another slide master with a different theme.
Your presentation currently has one slide master with a theme applied. To add a second theme, add another slide master with a different theme. Here's how:
On the View tab, pick Slide Master.
On the Slide Master tab, pick Insert Slide Master.
Tip The second slide master inserts and is automatically selected.
On the Slide Master tab, pick Themes, and pick a theme from the list.
The Slide Master you've added will now have a different theme from the other Slide Master in your presentation.