You won't believe what these Total Eclipse of the Sun stamps can do.

In honor of the total solar eclipse hitting our skies on August 21 (that's Monday!), the United States Postal Service has launched Total Eclipse of the Sun stamps. But the extra cool part? They actually change color. For real.

Related: Everything you need to know about the total solar eclipse 

Just place your thumb on the black disc in the middle of the stamp and you'll start to see an image of the moon peek through. So cool, right? And, the back of the panel of stamps shows a map of the eclipse across the U.S.A. If you're not planning on using them to send out your bills, you can preserve them with the protective sleeve you can also purchase for $.25. Such a cool way to commemorate this special day, and pull out the next time a total solar eclipse is visible. Of course, you might need two of them per letter if it takes as long as this one has to grace our sky.