The skybox is 'Devil's Punch Bowl', by Simon O'Callaghan, a.k.a Sock. I fiddled with the hue in Paint.NET and also shuffled the images around so that the sun was in the right position in the sky

Simon's website is currently down, but an archive of his skies can be found at https://www.slipseer.com/index.php?resources/socks-skyboxes.78/