A slow relaxed rhythm can be created with connection of color and lines. Colors can gradually intensify or become lighter or darker gradually. They can also create a rhythm through repetition. A faster allegro rhythm can be created by the vivid contrast of light and dark, by lines which abruptly change direction or which are broken and scattered around a room. Harmony is achieved, again, in much the same way as is musical harmony.
Concordant notes create a subtle sense of belonging together.
They create a comfortable feeling in much the same manner as does unity in design. Discordant notes create a tension, a slight sense of unease or being off-balance just as the use of variety does in a decorating scheme. Finding the proper balance of each with the other is the key to good design. You might try using a variety of treatments in a unified color scheme. Go through your decorating magazines and find several pictures dealing with each of the Principles described above.