Civil twilight - the period roughly 30 minutes before sunrise & 30 minutes after sunset (when the sun's center is less than 6 degrees below the horizon) - is usually the time for the most colorful skies. I submit today's PAD as Exhibit A. This image was made a bit more than 10 minutes before the actual posted time for sunrise on this date. A few minutes before & after this image was made those clouds were a whitish gray. Show up at the predicted time for sunrise & you've missed it.
For comparison, here's the situation about 1/2 hour later (different vantage point) when the sun actually peeked over the far hillside ("Peeked" nearly 1/2 hour after the "actual" time of sunrise due to the topology). http://www.pbase.com/ed_k/image/87463414 Here the sky is no where near as pretty. If you snooze - you lose.
I shoot this type of scene with an exposure compensation of about -1EV and a graduated neutral density filter in order to to supersaturate the captured colors. This is about how they came from the camera (not from post-processing). The gold grasses between me an the cattails make a nice base to complement the sky.