Went to Home Depot first and found some colours samples that I liked and intended to go back to purchase. Fortunately, we read the professional reviews of paints etc. Their suggestions were amazingly educating. We chose Sherwin-Williams and the staff in the store sure did not disappoint us; they were professional, pleasant, friendly and patient. We tried one colour first and went back, they changed the formula. Note that it was no one's fault, as paint colours do not look the same from different angles, or with different lighting etc. The price of their products might be slightly higher than those in the mega hardware stores', but the quality of Sherwin-Williams is surprisingly good. My husband is not a professional painter but he has done lots and lots of painting in the past 40+ years. He could tell the difference in the result of his painting job which made him very happy and proud of himself! He also loves their supplies as they help the painting job greatly in terms of effectiveness and efficiency.
I can go on forever, but don't want to take too much of your time. Good luck to all our fellow home owner-painters. When in doubt and if you are not aware of it, look it up on Google for professional and amateur painters opinions and experience.