Apply the selected background colour when adding a background image

Currently choosing a background image overrides any selected background colour.

As the CSS spec allows us to specify both a background colour and an image for a block either in the background shorthand syntax or as separate properties, it will be very useful for Cwicly to honour the selected background colour when a background image is selected.

Thank you.

Just bringing some attention to this as it when it is implemented it will help reduce the need for a few workarounds such as block nesting, z-indexed overlays or custom code.

@Louis, what do you think? (I appreciate, this may need a Legacy setting to prevent unwanted behaviour on existing sites)