If you want to personalize your form or tailor it to your audience, you can add a theme to a form.

Add a theme or color

  1. Open a form in Google Forms.
  2. Click Style .
  3. Choose a color for your form. Or, to add a theme, click Insert image .

You’ll see your new theme and you can continue editing your form.

Upload an image as a theme

  1. Open a form in Google Forms.
  2. Click Style.
  3. Click Insert image.
  4. Click Upload photos.
  5. Drag a photo into the window or click Select a photo from your computer.
  6. Click Done.

Information found above comes from Google's Docs Editor Help page.