To avoid variations in the final color, don't cut in around any more area than you can roll out in 10 to 15 minutes. It helps to paint with a partner. And don't stop for a lunch break in the middle of a wall. When creating an accent wall, paint light-toned walls first, accent walls last. It's easier to go over dark paint with light if you make a mistake.
Darker colors dry more slowly because they contain the solvent glycol.
Follow the manufacturer's directions about drying time between coats - sometimes as long as overnight. And keep the room well-vented. Not only does proper venting speed drying time, but it can also help waft away the stronger ammonia odors in many deep colors. Armed with this knowledge, take the plunge and experiment with color.