Ribbon Nav Bar

This example is Theme14-10 (which is probably the quickest option and then just change the Ribbon to the colour you prefer)

Or go to My Website > Site Layout (choose Layout 14)

On success page click > Site details change the Glow on Centre Bar to transparent/invisible

Return to My Website >  Colours, Backgrounds and Overlays > Overlay 3  Upload nav-bar grey (black or white)

Choose > upload another  

upload nav-bar-Panel 1 grey (black or white but the same colour as your choice from above) into Colours, Backgrounds and Overlays > Panel 1

Remember once you have uploaded them, go back into Overlay 3 and Panel 1 and actually choose the file you have just uploaded.

You may need to add or remove some of the transparent space to adjust to your own navigation and header font size