Circumzenith Arc

I'm putting this blip on for my mam as we were both shocked to see what looked like a rainbow in a bright clear sky with no sign of rain....

Confusing.

Turns out it was a Circumzenith Arc.

Taken from Weatherscapes.com

Q. I saw a bright rainbow right overhead, but there was no rain falling?
A. What you saw was not the rainbow, but a halo, most likely the circumzenith arc. Halos form in ice crystals, which are equally capable of producing colored arcs like the rainbow. These form in different parts of the sky, however. The circumzenith arc is caused by sunlight being refracted by ice-crystal plates floating horizontally in the atmosphere. The light enters the top face of the plate and exits a sideface.

Ok, so that doesn't make a lot of sense, but explains that we weren't going mad and actually did see a spectrum of light in the sky. I must admit, when my mam called me into the garden to see a rainbow, I thought she had her Stella goggles on....