Modify Admin Center Branding

Feature Request Summary: 

Being able to manage the branding (colors, logo, tab icon) for the Admin Center like we are for Support.

Description/Use Cases: 

When working in both production and sandbox environments, it is helpful to be able to quickly tell them apart rather than having to double check the url in the address bar. 

Business impact of limitation or missing feature:

I have accidentally recreated settings in the Sandbox when I thought I was in Production. Previously, I have often needed to double check what environment I am working in. It's not usually a substantial amount of time in one-off circumstances, but it adds up.