This dye was obtained by the Egyptians from the shell-fish Carthamus tinctorius; and by the Hebrews from the Coccus ilicis, an insect which infests oak trees, called kermes by the Arabians.
This colour was early known (Gen. 38:28). It was one of the colours of the ephod (Ex. 28:6), the girdle (8), and the breastplate (15) of the high priest. It is also mentioned in various other connections (Josh. 2:18; 2 Sam. 1:24; Lam. 4:5; Nahum 2:3). A scarlet robe was in mockery placed on our Lord (Matt. 27:28; Luke 23:11). "Sins as scarlet" (Isa. 1:18), i.e., as scarlet robes "glaring and habitual." Scarlet and crimson were the firmest of dyes, and thus not easily washed out.
Easton's Bible Dictionary. M.G. Easton. 1897.