The colors are really hard to say. Far be it from me to say that I am a purist, but there probably wasn't that much manipulation of colors on this photo.
Not to get semantic, but there are more ways to manipulate colors and saturation other than something like Photoshop. For example, by bracketing w/ probably -2ev underexposure you definately make the sky colors bolder than normal. And then the choice of white balance will impact the colors shown as well.
At the end of the day it is just about presenting a final image that is similar to what you were trying to express when you took the photo, or phots I am more concerned about that than presenting a perfect rendition of what was there at that moment.