A triad is a group of colors that are an equal distance apart on the color wheel, such as orange, violet, and green. A color scheme like this can be pretty if you choose a dominant color and mix only a bit of each of the subordinate colors with it. If this combination sounds awful to you at first thought, picture orange and violet crocuses growing in a lawn of fresh springtime grass. Better? I find that using color schemes that already exist in nature helps a lot if I am stumped for a good combination.
When I am selecting colors for a quilt, I often think of a landscape. If I have chosen a selection of vibrant "sunset" colors such as orange, yellow, and fuchsia, I will then choose at least one "ocean" color, like turquoise or green, to make sure that my quilt is color-balanced. This gives the quilt some cool areas for the eye to rest, and keeps the warm colors from overwhelming the viewer.
Above is a quilt I made using this kind of color scheme. It was a class project where we were learning to make circles without pinning or templates. Each block uses both warm and cool colors and the overall quilt shows (or is meant to show!) the progression from the pale light of dawn through to the glorious full moon over a deep blue ocean.

I've mentioned before that yellow and purple are two of my favorite colors. When these two colors are combined with green you get a beautiful and nearly endless selection of color patterns. These three colors also use my "hot" and "cool" theory - the yellow is a warm color, while green and purple (since they both contain blue) are cool colors. The three balance each other out beautifully. The quilt above, created in EQ5 shows these colors together. I have used various shades and tones of these three colors in every home I have lived in and in many quilts and small quilted home accessories.
At the moment my kitchen is a sunny yellow with some dark purple and green accents and accessories. My dining room is a deep eggplant color with yellow and green accents, and my living room will eventually be a very pale green with purple and yellow accents. The three rooms will flow together wonderfully. I am also introducing black and white into all three rooms in the form of pillows, curtains and dishes just to give me more colors and patterns to play with.
Try pulling out your three favorite colors and see if they can form a nice triad!
Have fun!
Kelly