The simplest way to fix a bad paint choice without repainting the whole room is to do a color wash. You will require a quart of paint and should be the same sheen as the base color. The best thing when choosing color combination is to stick to the initial color but you will need to apply the color wash in a lighter or darker shade. This would not take you to choose in the color store because you already know the color you want. If you want to begin with the color you use, you must first apply the color wash.
It is easy to do color washing but it might take time to complete. However, you have no reason to hurry because you do not want your work to look shoddy neither do you want to hurry and make the same mistake all over again.