Red rainbows occur when the sun is on the horizon (less than one hand), and are created in much the same process that causes a sunset or sunrise to look red. Also, with the sun at that horizon, the rainbow will be very high on the opposite horizon.

Light rays from the sun at sunrise and sunset travel long paths through the lower atmosphere where the rays are scattered by air molecules and dust. Short wavelength blues and greens are scattered most strongly leaving the remaining light rays proportionately richer in reds and yellows which result in the glorious sunsets and red rainbows.

Red rainbows are rare, one of the hardest to view but to make your chance of seeing one greater, search for rainbows within fifteen minutes of the suntouch.