I just discovered something today with Google forms.
It is possible to take a Google form theme and make it your own!
If you use the default theme, there is a CUSTOMIZE button.
From the customize menu, it is possible to truly personalize a Google form.
Images for the top of the form need to be 800x200. Otherwise, the image will be rejected.
Font type, size, color can be changed for all textual items.
A plain color or a background image can be used on the page.
The color of the form background can be changed.
Below is an example of 'personalizing a form'. The header image is one of the Google choices.