There is a good reason painters are fascinated with the wonderful clouds of sunset and sunrise. The color becomes amplified and the personality of the clouds is very easy to see. When working to record this you need to first look for the movement lines. Mark them immediately. It's a moving target so getting the important diagonals is key. After the lines are there enjoy making it alive. As long as you remember that the sky is a dome and respond to that concept the sky becomes a little easier to paint. Value matters as always. Have fun and relish the fact that with a handful of pastels or a few tubes of paint you can make magic.