There are also ways to get a multicolored look on top of a higher fired glaze surface using china paints. One project we did in my china painting class was to create a surface that looked like malachite. Since china paints are transparent a very interesting surface can be reached with multiple firings using different colored paints. The problem with china paints on functional ware is that the paints do contain some lead and so might not be acceptable on surfaces that come into contact with food.
Yes, thanks Joel for the challenge idea and the energy to keep it moving. Each challenge I vow to myself to make something to enter - but chicken out in the end. Those who participate come up with such beautiful projects I'm abashed. But it sure is fun looking at the great pieces braver souls offer to the rest of us.
For advice on china/porcelain painting, guidance to suppliers etc you might try contacting Marci Blattenberger at rxguitar@Comcast.net. She manages an online forum ppio.com which can also be very helpful.
I have used both homemade colored slips and Amaco Velvet underglazes in the Lana Wilson manner successfully. I believe that Lana Wilson does the same in the video you mentioned. Some underglazes are certainly opaque, probably not all.