Have you tried Print Background (color and images) in Page Setup - Format & Options? I haven't used that option in many years, so I don't recall how well it works.

Sorry for not being clear enough but I'm refering to work around in CSS to make this work by default without having to change the browser settings. Thanks

This is a Webkit specific setting that doesn't have a Firefox (Gecko) equivalent.

See also:

• https://developer.mozilla.org/en-US/docs/Web/CSS/-webkit-print-color-adjust

What's in the background colors/images that is so important to print?

I think if you really want control over the appearance of the printout, you would be better off pushing a PDF with disposition: attachment.

But some people have proposed CSS workarounds, for example: http://maxlapides.com/forcing-browsers-print-backgrounds/