This effect was generated in Filter Forge, a Photoshop plugin that allows you to create your own filters.
The idea here is to make an arc and be able to bend it smoothly. That's about all this snippet does. You can alter the colors and width and vertical position as well.
The original bend idea was borrowed from TaTa Pushkarova's Rainbow filter. I simply improved on that idea. Also instrumental in getting this bend correct was Ssamm. He helped me out a great deal! So, thank you to both!
Crag Kraellin Walters arc bend bar offset horizontal vertical color profile gradient