It's now official and on Amazon!  As indicated by the (temporary) cover, it will be in full color, just like WPF Unleashed!  As always, take the release date with a grain of salt because I haven't even written the whole book yet, but rest assured that it won't be out until after Silverlight 1.0 is finished.  Although considering that I was able to write .NET and COM 100 years before the technology was introduced, I don't really need to wait...