You can change the pre-set pattern and colour on your moodle page header and My Pages card for an image.
To do this, click on the course administration button in the top right corner of your moodle page,
and choose Edit settings:
Scroll down the page to Module summary images.
You can either drag and drop the image from your computer into the box or click on the icon for the file picker.
There are options within the file picker to upload a file from your computer, or choose from other repositories such as OneDrive, you can also select files from Wikimedia, this is an online copyright complaint repository.
Once you have selected your file, scroll to the bottom of the page and click Save and display, your image will then appear at the top of your page and as the Card image on My Pages.
If you are unhappy with your image, you can go back to the Course Administration, and Edit settings on your page, scroll to the Moodle summary images, click on the image and then click delete
You can then add a different image.
Please make sure that images are good quality and large enough so that they do not blur or distort when showing at the top of the page.