Over a period of about 40 years I think I have encountered only about 3-4 fabrics that bled enough to definitely cause a problem if I had used them in a quilt. I usually do prewash, but more with the idea that I might get variable degrees of shrinkage since I often mix fabrics from several different sources in my quilts. If the bolt ends on Kaffe Fassett fabrics do not specify "colorfast", why trust them any more than another brand? I believe his name indicates the artistry that goes into the work, and most likely his company would back the high dollar amount with top quality "ingredients". In other words, it's probably a good bet. Skipping the pre-wash step might not be as risky as with some cheaper product, but I might still wash just to avoid having to worry about those intense colors. In other words:
Don't wash = slight worry
Do wash = no worry at all.