These are real evening twilight colors in Colorado. This is about half of a wave cloud on the lea side of the Rocky Mountains (you can see Pike's Peak in the lower right). The upper level winds are trying to rip this into a series of lenticular clouds, but with the sun down, that isn't going to happen. Shot from Cherry Creek State Park, a few miles South of downtown Denver.
Canon 5D MkIII, EF 24-105mm f/4L IS at 24mm
Av Mode, ISO 800, 0EV, f/8, resulting in 1/25-sec., hand held
Raw conversion with DxO Optics Pro 9.1 with some dust removal in CS4