Le terme spirale se réfère en général à une courbe plane. Lorsqu'une spirale se développe en trois dimensions, on parle plutôt d'hélice.
Brown is the color of dark wood or rich soil. It is a composite color made by combining red, black and yellow. The color is seen widely in nature, in wood, soil, and human hair color, eye color and skin pigmentation. In Europe and the United States, it is the color most often associated with plainness, humility, the rustic, and poverty. It is also, according to public opinion surveys, the least favorite color of the public.