Indeed, it's telling that the first screenshot they are using to illustrate the problem is a iMessage screenshot, with a high contrast background image, only one message and images in a similar color theme as the background image.
If you want high contrast in your messages app...don't use a high contrast background image?
That picture just feels like a case study in why Apple drug their feet on features like that for so long. If you let people set a background and change the font, you're going to have unreadable purple comic sans over kittens within minutes.
If you want high contrast in your messages app...don't use a high contrast background image?