Each of your allies fall into the following classes.

Archer (Yellow): Can fire arrows from any distance at enemies in the same row.
Cleric (Green): No offensive ability, but can heal nearby allies.
Knight (Blue): Good defensive abilities, average offense. Their shields allow them to take reduced damage from ranged magic and arrows.
Soldier (Red): Good offensive abilities, average defense, but vulnerable to ranged attacks.
Wizard (Purple): Shoots ranged magic from any distance at enemies in the same row.