While monochromatic photographs are the most color simplistic (often just using varying shades of one color), there are other photographs which take great effort to limit the range of colors that make it into the 4 walls of a photograph.
In our experience we find that beginner photographers not only try to fit too much within each of their photographs, they also try to fit too many colors in each of their photographs. The results are often disappointing from both the photographers standpoint and the audience standpoint. The human eye doesn't want to work too hard when looking at a photograph. By limiting information and colors you can effective simplify your photograph and make it more appealing to look at. Notice how the lack of color clutter in the following photograph creates a dramatic yet simple and visually appealing photograph. This photograph isn't monochromatic as it uses black, shades of yellow and orange and shades of green to compose the picture, but it still has much more color organization than most amateur photographs. Color simplicity is one of the major elements that separate great photography from good photography. By organizing your colors more you can step out of the world of amateur photography and display your photographs on a much more professional level.
Many photographers don't know exactly what "it" is they don't like about their photographs when they get them developed or look at them on their computer screen. Well the good news is that often the "it" is simply the fact that the photograph is too busy with such a broad array of colors that it becomes distracting and annoying for the eye to look at.
Remember, painters place a lot of time on the concepts of color balance and color simplicity. Just because you are using a camera it doesn't mean you should ignore these subjects. By paying close attention to colors in your photographs you can create more appealing, more harmonious photographs that look good both to you and to your viewers.
Color & Perspective
Color Tinting & Shading In Photography
Color Psychology In Photography
Color Balance and Highlight