How can I customize my portal so that clients see their company branding instead of mine?

If you'd like your clients to see their company name and logo when they log in, instead of yours, you can turn on Client Branding.

To do this, go to the Customization tab in your sidebar, and turn on Client Branding:

Once this is turned on, any client assigned to a company will see their company name and logo at the top of their sidebar in the portal:

For information on how to add company logo to a client's company, please see here.