It's quite difficult to distinguish between a sunset and a sunrise just by looking at a single image. The two events are quite similar and you can't be totally sure of what you're watching unless you can see if the sun is going up or down.
That said, most people associate colder, softer and brighter colours with sunrises, and darker, warmer and more intense colours with sunsets. Technically speaking, that's not an absolute truth, but that's the way it goes most of the time.
So if you want to paint a sunrise, put some yellow in your palette, as well as bright orange, pink and blue. You can also make interesting contrasts using dark blue on the sky and yellow on the horizon. And if you want to do a sunset, use warm and dark saturated colours, like red, orange, magenta and purple.
Try to paint the sun (if it's visible in the image) a little higher in the sunrise and a little lower in the sunset. This will make it even more clearer what you're trying to depict.
Paco Rico Torres is a freelance illustrator living in Spain who's produced art for several card games, magazines, books and role-playing games. This article originally appeared in ImagineFX (opens in new tab) issue 104.