The colorful patch of rainbow is a sundog that appeared to the left of the setting sun.
Sundogs appear when sunlight passes through a thin veil of ice crystal clouds and the ice acts a prism, refracting the light. Sundogs often signal that rain is on the way. The colors are red on the side nearest to the Sun, shifting through orange out to blue on the outside of the sundog. Often sundogs can appear white.
Sundogs are also known as “mock suns” or “parhelia,” which means “with the Sun.” The most common name, however, for these bright lights that faithfully follow the Sun is sundogs. According to Greek mythology, Zeus walked his dogs across the sky and those “false suns” in the sky on either side of the sun’s disk were his two dogs.
[The above is my abstract or summary of an article on Sundogs from Almanac .com]

Nikon Coolpix P1000

crop to straighten horizon, minimal contrast PS