Make text highlighting possible for instructors

Because I select the featured post of the week, and students will be tested on the content, I realized it would be useful to have a highlighting tool where I could simply select a few lines in a student post to guide students that read the post (often with several responses). Such a tool probably should not be available to students because a few might go crazy marking up other student posts, but for someone in my position where I want to draw their attention to some statements or facts in a post, it would be very useful.

Because many students are such bad writers, it might also be useful to have a specific color reserved to highlight bad spelling and/or bad grammar problems too.