Default theme custom background doesn't fully display

[DJPaul]

The background of the BP-Default theme's background is a very light gradient. If you pick a custom background color, it looks like only the bottom-half of the page is styled to your choice because the gradient is applied to CSS background-image.

I think this can be resolved by adding a callback to add_custom_background() in functions.php and unset body { background-image: ...; }

[djpaul]

(In [3589]) Ensure custom background colour overrides default background image if no custom background image is set. Fixes #2971