You would not want to do equal 1:1 with the gray and the blue. The Royal blue is actually very strong, as a little of it goes a long way. The color will also take differently with the type of fabric being used. I was dying my SGB ROTJ cotton suit and the blue was really dark, while the ESB twill was much lighter, and they were in the same dye bath.
The best way is to experiment with it to get the color you like (AKA, be sure to get color removal as well).
All and all, you will not need the full packet of Royal blue for one jumpsuit.