I initially did sequential single pass runs to determine how passes were needed. That process is cumbersome, and if the GFUI or GF hangs up I had to start over. As long as the material under test (MAT?) is pinned down, the registration between runs was excellent.
The images in this post were from a single run: I take the vector data and simply make a copy right on top of the original and set it to a different color. Once its in the GFUI I edit the settings for each path.
One note regarding editing the number of passes: when you click on the box you get a popup with only three choices (1, 2, or 3). Overriding those choices is a little tricky - I backspace over whatever number is currently in the box, type in the new number, then left-click in the box - hitting the enter key will revert the number back to 1, 2 or 3.