It can be any color, but must have a minimum capacity of 3500 cubic inches. There are a wide variety of internal frame backpacks on the civilian market capable of handling abuse and with enough capacity for a self-sustainable DMAT mission of 72 hours. The key here is to minimize the size of the backpack to dimensions small enough to hold what you need. Remember, you may have to carry your own pack whatever distance necessary to accomplish the mission. Don't count on transportation to be avilable.
Most backpackers are in a constant battle to reduce the size of their packs.
Consider taking only what you need, based on the length of time you think you will need it. Unfortunately, this is something best learned through experience. This philosophy saves weight and space in your pack. Don't take more sleeping bag than you need. Once wet, they require a dryer before they are useable again.