How To change Header Color?

In Wordpress Admin Panel go to Appearance > Editor section

Open Editor

After opening Editor Section Click Toggle Navigation > Template Parts > Header which in on left top corner of Editor Section Screen.

Toggle Navigation

Select Template Parts and Open Header from available Template Parts.

Open Header

Once Footer is opened, click on List View from Top Bar.

Select List View

Under List View go to Header hierarchy and select Row. This should select the complete Header Block.

Select Row

Now go to Row Settings and Select Background under Color and change color

Change Background