modify header colour (background)

Hello, I can't change my header to a custom solid color. I wanted to modify the default header present in the compostions. You can see example on this screen capture https://drive.google.com/file/d/1NxO8cyi0iMTe9y1NznSDC5zFXjQEkqSB/view?usp=drive_link Is there an easy way to do this? thank you best regards