Hello there!
Unfortunately, seems you found a Bug.
Here is a workaround to change the Particles circles and lines color until we fix that bug:
1. Go to the Customizing ▸ Header ▸ Header Image
2. From the “Display Header Image On” dropdown list, select the “Everywhere”
3. Enable the Particles and set the Circles and Lines color per your wish.
https://prnt.sc/l4hni6
4. From the “Display Header Image On” dropdown list, select the “Nowhere”
5. Publish the Page.
Let us know if this steps helped you.
Thank you for the understanding and the patience.
Regards