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.
Being both motionless and emotionless, gray is solid and stable, creating a sense of calm and composure, relief from a chaotic world. The color gray is subdued, quiet and reserved. It does not stimulate, energize, rejuvenate or excite. In the meaning of colors, gray is conservative, boring, drab and depressing on the one hand and elegant and formal on the other, yet never glamorous.