Now that we have the basics out of the way (see http://allsortsartbyali.blogspot.com/2014/12/want-to-use-color-in-your-home-learn_93.html ), let's discuss how to get started actually getting color into your home. How much is appropriate? Is there a way to dip a toe in the color pool without going too deep?
When getting started, be patient. Don't just grab a swatch and decide you need 5 gallons of Passionfruit Sunrise, stat; first of all, don't ever just pick one color swatch. Take at least three (the kind that has a gradation of lighter and darker shades of the same color is best), and take them home with you. Look at them at your house, with your stuff. If your furniture clashes horribly with Passionfruit and you don't find this out until the whole place is drenched in it, that is not going to be happy times. Also note that the store's lighting is likely to be different from that in your home. As they say, "measure twice, cut once". The paint store is not going to give you the stinkeye for taking a half dozen swatches; they will probably breathe a sigh of relief that you are less likely to show up in tears, demanding your money back.
Once you have selected a color that seems to be the best fit, get a better idea how the paint will look by returning to the store and asking for a sample. Most stores will mix a small amount of color for a reasonable price; this should be enough for you to paint a decently-sized square on the wall. Be aware that paint can appear lighter or darker while it is wet. Allow your paint to dry overnight (use interior latex; oil-based paints and the solvents required to clean up after them are extremely smelly and not very good for you at all), which will "cure" it so that the finished color will be apparent. Please note that if you are using a new color that is significantly lighter or darker than the current wall color, you will need at least two coats (probably more in the case of light-over-dark), so you should paint as many coats as necessary on your sample area, as well.
If you are a bit more sure about the color, you can buy a quart and paint one wall. If you love the color but think the shade would be too overwhelming all over the room, you can leave that wall as an "accent wall" and get the next shade or two lighter for the other walls. Accent walls are commonly used to add interest to a room, creating a focal point to draw the eye, so choose a wall that would be a good place to display some prized artwork or furniture (the wall with the fireplace would also make a good accent wall, as that is already a natural focal point). You can even use color for one wall and leave everything else white.
If you aren't yet ready to commit to wall color, start small. Pretty easy; you don't have to make the leap to an entire honeydew-colored sitting room. If you aren't sure, just invest in some green accessories: some throw pillows, maybe a lamp. This will also help you satisfy your color jones if you are renting and your landlord won't let you paint. So, get a little color happening in your surroundings, and don't stress-decorating is supposed to be fun!
Image from freepik http://www.freepik.com/free-photo/color-swatches_390574.htm