grit n.

in reference to color, "intensity of distinctive hue, degree of departure of a color-sensation from that of white or gray," 1889, from Latinized form of Greek khrōma "surface of the body, skin, color of the skin," also used generically for "color" and, in plural, "ornaments, makeup, embellishments," a verbal noun from khroizein "to color, stain, to touch the surface of the body," khrosthenai "to take on a color or hue," from khros, khroia "surface of the body, skin."

Beekes considers this noun to be of uncertain origin. It sometimes is explained as being somehow from PIE *ghreu- "to rub, grind" (see grit (n.)).

"stone in small, irregular fragments," early 13c., from Old French gravele "sand, gravel; sea-shore; sandy bed of a river," diminutive of grave "sand, seashore" (Modern French grève), possibly from Celtic *graw- (compare Welsh gro "coarse gravel," Breton grouan, Cornish grow "gravel"), perhaps ultimately from PIE *ghreu- "to rub, grind" (see grit (n.)). Gravel-crusher was World War I slang for "infantryman."