International Trade & Bonding Commission regulations state that all items sent further than 40 miles from its point of origin must be colour coded to represent the products inside. In this case the products contained are medicinal goods indicating that the items inside are either refrigerated or are possibly dangerous maybe even both.
Medical goods crates contain items such as blood and plasma, pharmaceuticals, samples (eg. virus/bacterial samples) and even transplant limbs. Supplies of medical goods are often targets for raids as they can be worth a fair amount of money to people in the right markets.