"He who marches out of step hears another drum." ~ Ken Kesey
Since I believe that you do not sep this in house, or yourself, you should ask the person you are going to use. We all could give our opinion on how we would do it, but your separator may have a different approach and that is the one that will be impacting your profits.You could dictate to your separator that you want 4 colors and he can do it, but it would look better in more. Be careful tho, when giving the separator free reign to use as many as needed that fits on your press. This job could be looked at as 9 colors when it can be done as well in 6-7. It's kind of a customer level of quality question. How accurate do they want it and for how many shirt?I would prefer a min of 5 colors.YellowGreenLight grayDark grayRedIf using one gray, you would have a lot of dots in that lighter area. It can be done but how accurate does your customer want it?More would be even more accurate.
I think Frog was asking why include the light gray instead of just using halftone of the dark gray.