A triad is three colours that are an equal distance from each other on the colour wheel. The best ones use the primary colours – red, blue and yellow.
Linda Aman gives a wonderful demonstration on triads in her video. Watch how she mixes the colours on the paper. The colours obtained are more vibrant then if they were mixed in the palette.
Doris Glovier give an introduction to triads and provides three different triads and give illustrations of the difference. You need to scroll down half way through the screen to find the introduction. The top half of the article talks about a different mixes. I debated about using this article however; I felt that the different tirads she used as well as her samples were helpful.