This is becoming a hijack. Should move to map making.
I learn something new every day. I use color/no color patterns in the TYP files for land cover in Desert Southwest, but I thought you had to compile them with "Transparent=Y(or S)" to get them to read through to another map.
If the polygon for "background" is transparent, won't it behave like a transparent map?
I've never assigned a color (or no color) to a map background polygon. Always just set the transparency switch to "Y", or more recently "S" in order to hide the cpreview polygons.