I liked the NTDS scheme, but I liked even more the fact that you could choose. There are 6 such circles per unit, showing the range of its air, surface, and submarine sensors as well as the range of its air, surface, and submarine weaponry. They're probably just mimicing some military standard coding, but you really just have to memorize all 6 colors. This 'force analysis' is another area where the game really shines, although it threatens to overwhelm you in detail. If you click on the 'database' button, a window pops up giving you a one-paragraph description of the ship class, along with a little picture of the ship.
Aircraft have another layer of detail generally missing in ships and subs.
Aircraft, even aircraft of a particular type, can have various types of armaments stuck on them. Rather than load each weapon on a plane one by one, each plane type has a series of 'bundles', called 'loadouts', of packages of armaments. You can control which loadouts you put on which planes. After a lot of database surfing you know what forces you have and what each is good for. There are no less than four ways you can control your units - individually, as a 'group', as part of a mission, or as part of a formation.