The difficulty that may be faced by persons using screen readers is not that they will be unable to read it but depending upon the screen reader and settings they may not know that the background colour has changed. If the background is intended to provide context information (for example halloween colours of orange and black) it will still be readable but the context is lost.

Color blind people or those with low contrast vision may have a hard time reading text, however, so that's the main issue.

I think you mean screen reader.

If you type text directly into the Facebook status update or other text box, it will be accessible to everyone, even if you pick a colored background.

If you use a meme generator, it creates an image of text, and then blind users who use a screen reader won't know what it says.

The latest release of the Facebook iOS app has revealed the bg color post formatting to VoiceOver, the iOS screen reader. Now I hear specific colors or gradient styles announced just before hearing whatever text has been typed for the post. It's quaint, but really doesn't serve any practical purpose other than just getting in the way of the post information.

For colorblind or visually impaired people, the choice of the color bg and text will be very important, as certain color combinations are hard to read and contrast will be directly affected, making the overall text difficult to decipher.

I just don’t think that’s a necessary rule. Thanks for being considerate though. Hey more mods should? Hahahaha!