Little late answer...
Shutter functions are set inside Color Palette settings. Not in Automatic Training, but in advanced settings.
There you can manually set up all values for color signals, Shutter signal and Blanking. You can assign a separate output levels for every color.
The only way I see to solve your question is to choose only one color that will open shutter. All other colors have shutter closed.
Or, better way: You can set up 3 different palettes : balanced, bright and full-power.
Set up all paletes as usual, and then for 2 palettes close shutter for every color, and for 1 palette set shutter to be open for all colors (except black).
Then in showtime Track settings (or in LD > Frame advanced settings) you can choose which of 3 palettes to use. With this you control shutter.
I haven't tested this, but it should work.