This is a tiny rainbow, sometimes they'll go across clouds, sometimes they're behind clouds just so far away near the horizon. Sometimes fading out to light pastels, sometimes surrounded by dark dark grey skies.
A rainbow is a true gift of nature when you are already standing there with your easel, and ready to catch it. Here one fisherman remaining on the beach.
Most flee when the rainclouds arrive. I am most often still there with the surfers, a late dog walker or a few fisherman or nobody at all.
When they could film the movement of folks entering the beach from up a satellite, this too would be like a wave: in sunshine, a wave of dark dressed black dots entering the beach, clouds moving in, the first drops of rain making all the the 'ants' moving out of the area rather quickly. From a crowded beach to a total empty beach in minutes!
I teach about painting Seascapes in ► Seascape Beginner that's here and an online course more specific about Summer seascapes, figures and parasols is this one: ►Painting Summer Seascapes find this here.