The Exposure Value being too negative (-2 2/3) I had to use PSE 13:
Highlights and midtones
Contrast
Saturation

It started as a double ordinary rainbow around 20h25.
The sunlight filtering through the north-western clouds started changing
The outer colours of the sky beyond the inverted rainbow started changing from blue to darker blue to faint violet
from 20h30 to 20h33
The inner half circle colours turned from partial yellow at the left bottom around 20h26 to the orange filling the half-circle around 20h33.