The color spectrum of a rainbow is in the order
of: red, yellow, green, blue, violet.
We see red light from the higher drops because it is
directed towards the observer's eyes. Violet light is directed
above the level of the eyes so we do not see it.
In the lower drops red light is directed below the
eye level and violet light is visible to the observer. This is
why we see the colors of the primary rainbow change from red to
violet in the order from top to bottom.
When
the double rainbow is formed the double
reflection also forms an color spectrum but it is
reversed. The double rainbows color order is(from top to
bottom): Violet, blue, green, yellow, red. It looks just
like a mirror image of the primary rainbow. In this picture you
can see that the red is visible in the lower drops and the violet is
visible in the higher drops. The exact opposite of the primary
rainbow explanation.