Your Mack looks really nice. Sorry for your loss, and for the loss of a brother firefighter (Chittenango Volunteer FD, Sullivan Fire District #1).
Suggestions for improvement? Well, 4" hoses for the hosebed, or a hosebed cover would be good. If you decide to leave the hosebed open with no hoses, then it would be unpainted wood. The Mack 6-spoke wheels would be the body color as would the monitor (deck gun). The ax handle would be unpainted wood, and anything diamond plate would probably be natural metal colored (not painted). Check out Don Mills Models ( http://donmillsmodels.com/ ) for additional detail items.