SharePoint Online: How to Change Suite Bar Color?

Requirement: Change suite bar color for SharePoint Online site.

SharePoint Online: How to Customize Suite Bar Color?
By default, suite bar looks in a black or blue background and changing the theme in modern sites doesn't change the color or the top suite bar in SharePoint Online. To set the default color for suite bar according to your organization branding guidelines in Office 365, including SharePoint Online, follow these steps:

• Login to Office 365 Admin portal as Tenant Admin >> Click on "Settings" from the left navigation >> Select "Organization profile"
• In the "Organization Profile" page, click on "Edit" next to "Manage custom themes for your organization"
• Scroll down and set the colors for the Navigation bar, Text, and Icon, Accent. Hit the Save button to save your changes. Optionally, you can place a clickable logo on the suite bar from the same page.

This changes the suite bar color for all Office 365 applications including SharePoint, Outlook, OneDrive, etc.

Here is the Microsoft article on customizing suite bar: SharePoint Online: How to customize suite bar?