The watercolor calendar envelopes work well with other stamps, too. Here is the Quilled Heart stamp on envelope 778 (and the 2015 non-machinable butterfly on 779).
Quilling is the art of using scrolled paper to make 3D artistic compositions. Wikipedia has some info, but better is to google 'quilling' to look for images, many of which are stunning.
The Quilled Heart stamp is the 2016 entry into the USPS Love series. Digital images of this stamp do seem more vibrant and show more detail than the actual stamp, although it has grown on me.