We recently received the HX30 AR-15 magazines from Hexmags, and along with the magazines themselves were several different bags of colored followers and latchplates. A veritable rainbow of options, from Zombie Green to Lava Red, Panther Pink and Blackout, Hazard Yellow, Nimbus Blue and the default Hexmag orange mean a wide variety of options abound, especially with three magazine body colors availalble (black, tan and OD green).
One critical way this color-coding can work would be to designate an all-black magazine (black body, follower and latchplate) for .300 AAC Blackout, while retaining the OD green and/or tan body for 5.56 NATO ammunition. This instantly identifies the two different calibers to offer another layer of safety when using two different calibers in the same type magazine.
Another possibility would be to distinguish different 5.56 NATO cartridges: Green follower and latchplate for green-tip 62-grain HP, red for 55-grain FMJ and blue for 69-grain BTHP. At a quick glance, the shooter knows the type of ammunition in each magazine—so you don't accidentally grab a magazine with steel-core ammo and punch nice, clean holes through a steel plate (not that anyone's ever done that, nope).