From the very moment I started painting minis, the color schemes were influenced not only by the story of the army, team, etc., but also by practical needs on the gaming table.
Often this meant coming up with color schemes, basing, freehand, or other hobby methods to help distinguish one type of unit or figure from another rapidly, even in a scrum.
Lord of the Rings turned out to be one of those potential 'scrum' games, with many different individual figures in a larger swirling mass of combat.
To tell the 'regular' Easterlings from the Dragon Knights, I used dark blue on the Dragon versions, with a more 'traditional' red scheme such as this for the standard pikemen.
This was very crucial, since in LOTR, you need to know exactly who is standing behind the first set of figures offering support. It's important to know right away the relative fight skill of the two figures potentially working together.
The Dragon Knights would be out front with sword, shield, and the higher fight skill, with the less talented, but still deadly pikemen behind.
The one thing in common between them was the purple of the headdress.
It was just enough to link the two together!
A few more pikemen and the banner...
And a set of the Dragon Knights on foot.
The armor of the Dragon Knights also had a warmer gold tone, while the underlings had more bronze/brass coloration.