Avoid the Big Box stores and shop at a local specialty paint store. You'll pay a few bucks more, but they'll often let you bring home small sample quantities of paint for free to test on your walls. Roll on a good amount of it and let it stand for 24-48 hours, in different lighting conditions. Try a few different colours to see how they look when they're actually on the wall. That's the only real way to tell.

Find the colour you like on the fan-deck and then buy one-shade lighter.

Places like Lowes let you buy sample mixes. I know valspar colors come in a sample size which makes life a lot easier. From a tech stand point, take a photo and apply colors you like in photoshop. When you find one you think is good - get the CMYK and google for CMYK to Pantone. LOL

Remember colors will look different not only in different lights but in those lighting situations at different points of the day. ...no matter what color you get.

You're not alone, color is one of the toughest areas for my clients. You can never tell what a color will look in your space unless you take the time to sample it in your room. Colors will go up twice as dark or bright as they appear in those little chips. You should always try a few versions of the same color. I suggest buying the small sample pots and painting them on sample boards that you can buy at the paint store. Painting it directly on the walls will be influenced by the color underneath. It seems like a lot of work, but you will know exactly what it will look like in your room. Good luck!

Don't kick yourself! It's because you are good with color that this is so hard. It only feels like it's a failure because paint is a lot harder to change than adjusting a hue in Photoshop. I'm the same way, and it took a long time for me to accept the fact that I'm just a color perfectionist.

In addition to segacs' great tips above, I'd also offer this:

1. Go with your gut over your head.
2. Roll the paint on one wall first before you do any edging. As soon as it starts to dry, you'll know if it's right or wrong. If it's wrong, you'll only be out 10 minutes of work.

I will add another suggestion, color look different next to another color... so take into account your furniture and the theme of the room you want to paint . I suggest to think about a palet for the room, like this even if your are a shade lighter or darker next to to full color scheme of the room that will feel less of a mistake.... ;)

I hired a color specialist. I highly recommend doing the same. It was $250 for an hour of consulting based on photos I provided and it's the best money my fiancé and I have spent on our renovation/redecoration. EVERYBODY comes in and wants to know what colors they are so they can duplicate it. You can see her website at: mariakillam.com.

As a graphic designer, at least you know when a colour doesn't work; most people don't. It's a common problem.

My best recommendation is to try full spectrum paints, like Donald Kaufman Colors.

I found his paints one rainy day when I ducked inside the Calvin Klein store on Madison Avenue. It felt like a religious experience; I kid you not. The walls just glowed, even on that rainy grey day. The light was so beautiful... Anyways, I did my research, and learned the store was designed by John Pawson (who, based on this store, was asked to design a monastery in the Czech Republic, so I guess I wasn't the only one who had that experience there!), and that Donald Kaufman made a custom color for the walls, and so I bought the paint "chips" for his custom line, and used that for our house.

Full spectrum paints use 8 to 16 pigments, as opposed to the normal 3 or 4. My experience living with it is that even in low level light situations you get interesting colors, but your walls never get shadowy or grey. If you use a dark color, the color gets more intense and complex; when bright sunlight shines on the same spot, the paint reflects different pigments and it looks like a totally different color. Gorgeous.

I also highly recommend ktColor, which uses intense, high quality, pigments (the source for Yves Klein Blue, as well as shades developed by le Corbusier), and Fine Paints of Europe (who have some amazing fan decks to work from).

Sorry, I bought the paint chips from Donald Kaufman's commercial line. They are pricy, but big and made with real paint, so the colors are true. You can also order sample pots.

I work in design, but I only got good at choosing paint colors after I spent a few years pursuing oil painting. I find it easier to think about rooms as paintings rather than design projects. Painting is all about seeing - graphics are about communicating. Here is the truth of color in the world -- it is 100% dependent upon the light. An object can appear white, black, green, red or yellow depending on the light that falls on it. The northern hemisphere light tends to be cool. So bright areas are cool and shadows are warm. In interiors, we think of bright cool colors as fresh, where warm deeper colors are often referred to as cozy.

So my advice is to truly look at and analyse the lighting in the room. Grab a white vase, a gray box, a black shoe -- somethiing neutral. Set it in different places around the room and see what you see. Are there jade greens, ultramarine blues, or vermillion reds showing up in the shadows and highlights? Make notes. The colors you see in the highlights are your dominant tones - the shadows will hold their opposites (for example, if the highlights look like ultramarine blue, chances are your shadows will hold some vermillion red-oranges).

So now, pick a paint color that coordinates with those tones in the room - for example, if you are seeing a lot of warm blues, pick a color with some warm blue in it. I would also say that the larger the wall area, the more neutral it should be. Let your furniture and accent pieces offer up color. Small rooms or alcoves are places for intense color choices.

If your home has little natural light, you should pick the color you want, then go one step lighter on the color chip strip.

It is definitely worth it to pay for good paint - Benjamin Moore or better. The paints have more pigments, and more varieties of pigments, so they shift and glow throughout the day.

Maybe part of the issue is understanding your lighting. In an north-facing room with tree filtered light, a color will appear cooler because the indirect sun through the leaves will add green undertones. That same color will look much warmer and more golden in a west-facing room with a sunny exposure. Or, if a window faces a neighboring building, the color of the building can change the light: my bedroom window is 5 feet away from a brick wall, and it definitely -- though subtly -- adds some reddish tone to the room.

Ha, and now that I think about it, my mom recently told me how much she loves the color of my kitchen. Confused, I told her that my whole apartment is the same color. She had always thought my north-facing living room was slightly leaf green and that my kitchen was a warm cream color.

And don't forget about a graphic designer's best friend, photoshop. I've used it to determine size and spacing for hanging up artwork, but it would definitely be a useful tool for color, too. For one, it might actually be easier to judge your room's lighting tone in a photo than with the eye. You can zoom in and see what kind of color noise is in there on the pixel level. To go the next step, you can do some masking and color work and actually mock up the room with your color choices. It might be more obvious in a mock-up if a color is too bold or not quite the right hue.

@Parnassus, great point about painting. There are things about color that I never thought were complex or interesting until I had to explain them to someone. Like someone once asked me how to match the magenta shade of a flower she was painting using cadmium red. To me it was obvious why it wouldn't work, but I had to dig up a tube of crimson and mix several shades of pink before she understood why she couldn't get bright pink from an orange red.

I know what you mean, colours on web or even print comes out different on walls. I believe it has to do with lighting. Most indoor light are slightly yellow/orange. I usually choose a slightly cooler shade to compensate. Also, colours are usually a lot richer when it is painted and dried. I would therefore also get a slightly lighter shade.
You can also buy large sheets of swatches from Home Depot. They are about 18"x24", it gives you a better idea how the colour looks.

@mschatelaine, nice writeup.
Here is the link to the Novy Dvur Monastery: http://www.johnpawson.com/architecture/monastery

I would really consider hiring a designer if you are painting the same room over and over. I'm sure with their experience they could help and it would be worth the money. It won't cost you much either.

What do you recommend for a low light room with green undertones? What shades do I need to make to counteract this?