In Yellow, The Thalmor have a small force consisting of elite well geared soldiers, many of them wielding magic.
In Green, the Forsworn are a strong force displaying unique gear yet lacking magic users. Their strength is mostly local, like their objectives.
In Red, Imperials are a large force of various quality, beginning rather poorly geared. On the other side, they may benefit from special training to raise their troop quality above others.
In Cyan, Stormcloaks are a large force of various quality displaying many kind of troops. Their lack of magic user may be corrected with the help of the Winterhold college.
This is great!