A reply from Richard Berry on the AIP4WIN forum, below, confirmed the point I made in my 2016-07-04 post;
Yes, they are added. This avoid any integer roundoff.
If you want to, you can use Red=Grn=Blu=0.33333.
I quickly tried his suggestion using an uncalibrated image and it seemed to work. What I need to do now is use this method to calibrate an image and see what results I get in Astrometrica.