Create a hero part with transparent image over bg colour

Hi I'm trying to use the hero header to:
*Retain the bg colour
*Retain the paralax effect
*Use a transparency and have it overlay the bg colour.

If I remove the colour or change it, or even change the opacity I can see the image. If I use my bg colour, the image seems to disappear behind the overlay colour.

Is there a way to do this? When you look at the site now, the overlay colour has been cleared and it's using the site defaults. The area above and below the image is the colour I need to have behind the transparency.

Thanks
AK