We did this craft with my two boys and their two friends this past Monday. I really wouldn't call it a craft either - its beautiful art work! I think I am going to frame three of them and put them on the walls. I just love them and they had so much fun doing it. You just watercolor on wet paper a background color and then when that is dry you give them a dab of india ink at the bottom and a straw. Sometimes you need to add a bit more ink further up.
Wow what great colors they did. Love it. I found the idea on this web site if you need a bit more help. I wasn't as formal with the tape as she was. I found her site through the crafty crow blog which I can't recommend highly enough. SO many ideas.
I might try these smaller, on cards. Change the background colors to blues and you could have a really cool winer scene for christmas cards.