A single sheet with wording on it is printed, then traced onto a new piece of paper with the white colored pencil and then water colored over. Although it's a few steps, they could all be done together (trace them all, then paint them all). Sure you can hand make envelopes if you desire, but I'm all for purchasing those in the name of saving time.
Alter your water colors according the season and you'll have a pretty look and idea for any time of year. Heck, forget the invitations and just give them a simple word like "Peace" and make your own holiday cards while you're at it. They'll even be frame-worthy year round if you play your cards right. Check out all the step by step details to this project over at Glamour and Grace.
Image: Glamour and Grace