The beginning of civil twilight is when the "color" starts to happen, so I usually arrive at my shooting location during nautical twilight and shoot until sunrise. Play this scenario in reverse in the evenings. An insiders tip for Mt. Rainier is that because of the huge vertical relief Rainier has in relation to the most of the state, expect the sun to hit the summit 10-15 minutes before official sunrise. Have fun playing with those online tools and be there when the "show" happens. I hope to see you on the mountain.
Adam