What does Boxing Day have to do with boxing?
"Dianthus Caryophyllus," commonly also called "pink," herbaceous perennial flowering plant native to southern Europe and abundant in Normandy, 1530s, of uncertain origin. The early forms are confused; perhaps (on evidence of early spellings) it is a corruption of coronation, from the flower's being used in chaplets or from the toothed crown-like look of the petals.
Or it might be called for its pinkness and derive from Middle French carnation "person's color or complexion" (15c.), which probably is from Italian dialectal carnagione "flesh color," from Late Latin carnationem (nominative carnatio) "fleshiness," from Latin caro "flesh" (see carnage). This carnation had been borrowed separately into English as "color of human flesh" (1530s) and as an adjective meaning "flesh-colored" (1560s; the earliest use of the word in English was to mean "the incarnation of Christ," mid-14c.). OED points out that not all the flowers are this color.