If no background color is set, the background color is transparent. But the whole site background color is white, so if you choose white or a color that is nearly white as font color the iframe appears so be empty.
This commit implements a new function that tests if a hex color is nearly white and if yes the code will change the background color to a grey color.
Not really any strong opinion
Thanks for the PR @fdellwing - the idea and improvement looks good to me :+1:
Would it be maybe doable to have a UI test to test for this behaviour?
Maybe not needed a UI test for this?
a UI test is not needed