This customization requires administrator access to the O365 Admin Center.
STEP 1: Navigate to O365 Apps and select Admin Center.
STEP 2: Once in Admin center, expand the left menu and select Show All.
STEP 3: From the left menu, expand Settings and select Organization Profile.
STEP 5: In the main area of the page, scroll down to the "Manage custom themes for your organization" section and select Edit.
STEP 6: In the Navigation bar customization window that appears, complete desired customization fields:
Click upload to browse for your logo. Pay attention to the file size and dimension requirements.
Enter the URL for your SharePoint top level site home page (i.e.: https://yoursite.sharepoint.com/ ) in the URL for clickable logo field.
Click upload to browse for a nav bar background image (if applicable). Pay attention to the file size and dimension requirements.
Click the Accent, Nav bar, and Text and Icons color boxes and replace the Hex value with your preferred colors.
STEP 7: Scroll down to click Save when finished.
On the next window that appears, click Close.
Note: It may take a while for all the applications in your O365 environment to display the change.
Note: If any individual users have applied custom/personal themes to their O365 applications, those users may not experience your top navigation branding.
Note: If a SharePoint site has a custom theme applied, that site will not display the branding.