Mobile menu icon invisible when using homepage banner image with dark background

Problem/Motivation

For the drupal.be website I set up a homepage banner block with an image to the left. The image contains a rather dark background.

When checking the site on mobile, the hamburger menu was not visible, because it consists of black lines.
I have resolved this by choosing another image for the homepage banner, but it took me a few week until I noticed.
So preferably we can provide a fix for this, so that the hamburger menu is still visible with a dark background image, or alternatively, provide a warning to content editors to make sure they do not use such an image, as to not break the experience for mobile users.

Steps to reproduce

- Edit homepage
- Edit "Homepage banner" block and upload an image with a dark background instead.