The image is stamped on the front of the vellum using Versamark Ink and then embossed with white embossing powder.
You use markers to color the image on the reverse side of the embossing. No need to be super careful when you color it in, just stay inside the lines.
In order to try this, I just grabbed the first stamps I found that I knew would emboss well. I used Stampin' Up water based markers to color in the images. You'll need to let it dry for a couple of minutes before handling since they're water based.
Not a very fancy card by any means but a good reminder of a technique. The colors are more muted than they appear in the photo.