About Double Rainbows:
What's happening here is that the ray of sunlight bounces twice off the back interior surface of the raindrop before re-emerging into the air.
The second reflection inverts the order of the colors – the secondary violet band forms at 54 degrees, the red band at 50.5 degrees – so the secondary rainbow appears above the primary one, with red on the inner edge and violet on the outer.
Because the twice-reflected light has had two chances to be transmitted out the back of the raindrop rather than reflected back toward the observer, the secondary bow is much fainter than the primary and frequently cannot be seen at all; it's typical for a secondary rainbow to be visible only at certain points along the arc.

GO 2... http://bit.ly/1vAjY1Q