How To change Header Color?
In Wordpress Admin Panel go to Appearance > Editor section
After opening Editor Section Click Toggle Navigation > Template Parts > Header which in on left top corner of Editor Section Screen.
Select Template Parts and Open Header from available Template Parts.
Once Footer is opened, click on List View from Top Bar.
Under List View go to Header hierarchy and select Row. This should select the complete Header Block.
Now go to Row Settings and Select Background under Color and change color