Sunrises seem to have a richer yet colder set of colours than sunsets. I used to assume that the cold night air was the trigger, but cold air is denser than warm air and surely dense air will turn the light more red. There are reds in the sunrise of course, but also acid yellows, mauves, salmons and bruised purples. The morning clouds can be alive with fire-colours but their edges still mix bruises with pastels.
The sunset on the other hand is predominantly red, grading to purple in good order, only varying in the intensity and breadth on the horizon.
Perhaps the night cleans the air of human detritus, leaving us to enjoy the natural beauty of the sky, while the day leaves the sky battered and bruised.