From Jimdo Help

Click on the "Colors" button on the settings bar to the very right to prompt the window containing the color settings.

Color templates

Here you can choose from a number of color schemes, if you don't feel like creating your own.

Personalized colors

Here you can select a color for your website's background and the font color (black or white).

Note: When you're asked whether or not you want to accept the new colors, click "Yes" to confirm the changes, "No" to discard them, or "Change" to select different colors.