Tym Altman (images, rainbow) at Vancouver, Canada. At right an Intense primary from one reflection inside the raindrops. At left, the fainter reversed colour secondary from two reflections. At further left a very rare sight indeed - the purple bands of supernumeraries from the secondary bow. ©Tym Altman, shown with permission
Primary supernumeraries, purple and green arcs inside the rainbow are a common sight whenever raindrops are small as towards the end of a shower. Those outside the secondary bow are almost never seen except when manufactured by hosepipes and lawn sprinklers.
Interestingly, there are only faint traces of a supernumerary inside this primary rainbow. The visibility, or not, of supernumeraries depends critically on the local concentration, raindrop size and raindrop size distribution. These can change quickly.
Right: Supernumeraries as we never see them - from a sun shrunk to a point to avoid blurring and raindrops all 0.75mm diameter. A calculation by AirySim.