If you head East from Þingvellir and reach the height of land, and the turn off to Laugarvatn, why not stop and wait for the sun? This is elf country. They just might show. What you are looking for are rainbows almost invisible as the sun disperses the mist like a breath.
And if they don’t show, waiting is also arrival. It all depends upon which country you arrive in. Care to try? You’ve got nothing to lose!