For any theme (both the Mentimeter default themes and the ones you’ve created), you can also style individual slides if you’re on a Pro, Conference or Teams plan.
To do this, select your slide in the Overview panel to the left and then select the 'Customize' tab. Now, you can add a background color or upload a background image. You can also change text, line and visualization colors to customize the look of your slide.
These changes will be reflected in your presentation view only. The styling that is added to individual slides will not be reflected in the voting device.