Gah! I tried it again with one particular file. I made sure all the contours were closed, applied a RVW color, saved it, and then brought it into the other (new) computer in X5 and sure enough, it was black.
When I click on it, the color info at the bottom right of the screen says: "100% unknown color".
Again, X5 has the RVW pallette built in. What is going on here?