Different trainers and regions will assign different meanings to different colors. Many military systems are coded blue, or protective. The military alters all are called up periodically to reinforce blue training. If the trainer at a later date wants to access a blue system, they may call them up by color, or wear a piece of clothing or a scarf in the color they want to reach. This becomes an unconscious trigger for this color to come forward.
Color coding is one of the first methods that is inlayed over systems.
Because it is so similar to jewels programming, I will discuss how it is done under jewels. Jewels is considered higher than metals, and more difficult to obtain. Basically, either metals or jewels is a form of reward based programming. The child will be eager to look at it, touch it, and is encouraged to by a trainer with a soft kind voice. The child is usually eager to be.