A red rainbow is rarer than a multicolored one
Rainbows are not exactly a common sight, but monochrome rainbows are an even rarer one. They are formed in an almost identical way to their multicolored counterparts. The only difference is that the red ones only happen when the Sun is close to the horizon.
The Sun’s low angle means that the light has to travel a longer distance through the atmosphere, which causes the shorter wavelengths, such as blue, green, and yellow, to be scattered. The red rays are the ones that are primarily left behind.