Text Edit coloring entire page instead of selected text

Used to be that you'd highlight specific text, choose a color, and just that text would get the color. For some reason, now when I do that, regardless of which text is selected, the entire page of text gets the color.

Is this a setting, or what else may I have done inadvertently to cause this? Old documents are fine, but all my new documents do this. What's up? Thank you!

[Re-Titled by Moderator]

Original Title: Text Edit colored text