|Contrail Ice - A 22° parhelion (sundog) lights a contrail. Imaged in Finland by halo expert Jukka Ruoskanen (Views of the Sky). ©Jukka Ruoskanen, shown with permission.
Contrails are clouds of water droplets (sometimes supercooled) or ice crystals. These latter on occasions form vivid halos if they are large and optically good - and the trail position relative to the sun is just right.
The sundog colours are well displayed with deep reds towards the sun.
The greens and blues are more pastel because at their angles they are overlapped to some extent by yellows and reds.
Sundogs are produced by hexagonal plate crystals with a whole range of rotational positions and consequently each colour is spread out from its minimum deviation angle.