How To Change The Colour Without Changing Form Of Header

I want to change the colour of the header but keep the curved corners as they are and keep the white spaces below and to the sides of the header. But as soon as I change the header colour everything next and below the header as well as the header becomes the same colour. https://screencast.com/t/DPF0P57pC

Any idea how I can resolve this?

I am using the real estate responsive theme with RT1 child theme.