Glad to have you here, userpetercon.
Let me first welcome you here in the Community.
As of now, changing the background color of QuickBooks Online isn't possible.
For now, I recommend visiting our QuickBooks blog from time to time. This way, you'll be able to stay updated with all the latest news and product updates.
Additionally, I encourage checking our Help articles page to learn how to manage your QuickBooks account. From there, you can read articles that can guide you in completing your task.
If you have any other questions, please let us know. This way, we'll be able to help you out.