Ok, So we're going with sport grey or Charcoal shirts, Black, White & Green ink. here is a screen capture of my seps and comp. You can see my channels.... Most of these are selection masks..... so you can select an area, minus or intersect another from it....
Then I select the gray scale and paste onto the color channels.... the real magic is applying curves.... we want the green to tint up when mixing with the white and tone down where mixing with black... But we want there to be no green in the darkest or lightest areas.