Interior designers, and others who work with interior colors, have noticed that color schemes tend to fall into natural categories.
These categories can act as guides to help us think clearly about the colors we use.
In practice you'll find that these groups overlap - your scheme is mostly one group, but can use the ideas of another group as well.
This is where you take one hue and use it in a room, but you vary its tone and intensity.
It may sound a simple idea, but you can have a vast range of interior colors. In fact, the colors can be so different you might not recognize the effect as monochromatic.
You'll probably find you're able to get more interesting effects with yellows, reds and oranges than with deep blues, violets and greens.
Yellow is a very versatile color. A soft, muted yellow turns to a grey-green. If you then deepen the tone it turns olive-green, giving no hint of its yellow origins. On the other hand, if you take a blue-green hue and shade and tint it, you can still see it's basically a blue-green.
You may worry that just using a few subtle variations of tone and intensity will leave the room a bit 'flat'. One way of giving more interest is to use textures which can give a strong contrast. Stone, glass, stainless steel and marble, for example, can all add interest to your room. Or if you have a traditionally furnished room, items such as brass standard lamps, plants and gilt picture frames give just the right amount of textural contrast.
If you take hues which blend into one another on the color wheel, you'll find they blend well in your room color scheme. There is more variety to this than you might think.
The reason is that you don't have to keep the tone and intensity the same.
So if you chose a pale green, and then used a slightly bluer version of it, you'd have harmony of hue (the hues are close together). Now reduce the intensity of the blue-green until it looks 'dirty'. You still have harmony of hue, but a very different effect.
In the illustration below, the right hand color of each pair are all the same hue as the left, but with varying tones and intensity.
Tone and Intensity Harmony
But, you may ask, is there any advantage in keeping the tone and intensity the same? What happens is that you can safely mix a much broader range of hues.
The result is that you can have schemes in which the colors have a pleasing relationship with each other, but they don't seem to follow any particular rule.
The Victorians used this a great deal, keeping their hues fairly muted, and the interior colors all looked as if they belonged together. You'll also see this effect used in many modern fabric and wallpaper designs. If you see a design which looks 'complete' but the colors don't have an obvious connection, chances are this is the method used.
The colors in each column in the illustration below are the same hue. Those in each row have the same settings for tone and intensity.
If you find yourself unsure which colors to select for your room, there's a way of making sure you pick the right ones for the task. It's been developed based on the experiences of decorators over a long period of time. (Only for the USA and Canada.)
The Shortcut to Perfect Paint Colors - Paint Color Cheat Sheets