How to make facebook post with white letters on colored background

I see some facebook posts with a large colored rectangle and the (large) text in white. How is that done?

If you’re on the normal site, when you start a post, there will be a rainbow colored square icon with an “Aa” on it. Once you select that, you select a square with the background color/pattern under where you type. Select one and there you go.

On mobile and app, the background squares are already there.

There is a character limit though before it turns into a regular post though, I’m not sure what it is, but it’s rather short.

I’d use it far more often if it weren’t for the character limit, which, as Ashtura mentioned, is quite short.

I think the intent was to have them be more meme-like, which doesn’t exactly fit a long post.

I’ve seen some people on my FB have figured out a way to defeat that and are able to make long posts in the center type mode. So long in fact, that you have to click 'read more" is you want to read the entire post.

I’d LOVE to know how they do that.