You can change that background color of page heading by following these steps:
- Go to Dashboard -> Pages -> All Pages
- Select the page you want to edit, you will redirect to page editor
- Scroll down to bottom, you will find a box titled “Page header Section”
- Click on “Background Color” and change the color
- Now, Scroll to top to “Publish” metabox
- Click on “Update” to save the changes.