Here’s how to customize the themes with your own color combinations.
In a new presentation, select a theme from theThemessidebar on the right.
Alternatively, go to the toolbar and selectSlide>Change Themeto display the same sidebar with all available themes.

SelectSlide>Edit theme.
SelectColorson the editing toolbar.
choose the drop-down menu and choose the slide element.

For instance, Text and background, Accent, or Link.
Pick a theme color for the element.
Choose from various pre-set colors or use theHueslider to experiment with a custom color.

Note:
Every slide that uses a particular color will update to the new color.
These color changes will only be applied to this theme and will not create a new one.
Select one of the colors under theDefaultcolor palette for a default color.

For custom colors, drag theHueslider for the color you want to use or enter a hex value.
Use the same steps to change theme colors for all the different slide layouts and the specific colors.
How to Customize a Color Palette
Google Slides themes allow you to customize the default color palette.

But you could save the presentation and reuse it for future slides.
Open a new Google Slides document and selectImport themeon the Themes sidebar.
grab the saved presentation with the customized theme colors and apply the theme to your new document.

Choose the slide you want to change, then from the top of the screen selectSlide>Change background.
Note that this will change the color of the bulletandthe color of the text connected to it.
