Nematode Body Structure. The phrase tube-within-a-tube is a convenient way to think of nematode body structure, and also a term used to refer to a major trend in the evolution of triploblastic metazoa (Brusca and Brusca, 1990 Invertebrates).
Neutrals and Universal Colors. Let me explain in details... In general, neutrals include black, white, gray (mix black with white and you've got gray) and different shades of brown. Nowadays a color can be called a neutral based on how effectively it can blend in with other colors. Basically, they match with all colors and color combinations - and don't create much of an emotion.
All About the Color GRAY. Gray is the color of intellect, knowledge, and wisdom. It is perceived as long-lasting, classic, and often as sleek or refined. It is a color that is dignified, conservative, and carries authority. Gray is controlled and inconspicuous and is considered a color of compromise, perhaps because it sits between the extremes of black and white. Gray is a perfect neutral, which is why designers often use it as a background color.