LIGHTING!!! Lighting is so so important. Before you even pick the color, you have to factor in how much natural light the room gets. Other random factors- Flooring. If you have a whole house full of cherry wood, your paint colors will reflect it, making everything look slightly pink. If you have a ton of windows and a forest of green out the windows, the green tint WILL change the colors in the room. Fortunately, changing out the light bulbs can balance out any of those factors. The best situation would have a ton of natural light and a mixture of layered light (recessed, overhead, task, etc)
That being said, if you live in a cave, you can easily simulate that scenario. Picking out the light bulbs for the space can be a game changer in regards to color for your walls. I'll break it down for you...
Incandescent bulbs- are most commonly used. They're cheap and available pretty much anywhere. They also have a warm glow, leaving a yellow tint on paint colors. This bulb will make your whites appear cream and your blues appear green, etc. Cool colors look horrible with this type of bulb.
LED-... what am I a Rockefeller?
CFL's- like incandescent but last longer. Leaves a warm glow. the slight down side... these bulbs contain chemicals that can eat through your skin if broken. Buuuuuuuut, they're RECYCLABLE! So that totally makes up for it, right? ;) DONT GOOGLE IT. THE IMAGES ARE DISTURBING.
Fluorescent- We all know these from cold office buildings. These generally leave your paint looking blue or green although they are manufacturing some now that give a warm tint. They can't be put on a dimmer but I have 4 kids so romance is not an option anyways.
Halogen- These bulbs are the only bulbs I buy. They simulate the closest light to "natural daylight" and don't corrupt your paint color choices as much as the others do.
So before you get all mad and change your paint color for the 18th time, try changing the light bulbs in your space. I promise it will dramatically affect the color of your paint.
Also, here's a pretty picture of my old kitchen and the antique chandeliers I used above the island. Because I can't do a post without a photo. Note the natural light that was EVERYWHERE in that house. I miss that. Sniff. Oh, and by the way, the paint color here in called chocolate froth from Home Depot. I think it's a behr color. It was the perfect greige for a home with a ton of natural light.