Rainbows are circular with blue being in the inner arch. So it does look like a rainbow. Rainbows can certainly be brighter than the sky behind them--I have seen several. There also appears part on another image inside the rainbow at the top of the frame. So it is very possible that it is a rainbow image.
Originally Posted by RalphLambrecht
However, if it is flair, how does it produce a circular refraction pattern with a distinct spectra?