The headword Bosor, which appears in that form throughout the
Septuagint (beginning with
Deuteronomy 4.43) and also in e.g. the
New Testament (
2 Peter 2.15) and
Josephus (
Antiquities of the Jews 12.340), should more accurately be "Botsor", a variant of "Botsrah", the town בצרה of the Edomites that was destroyed with great bloodshed, leading to the image of God as a warrior dripping blood after having "trodden the winepress of Botsrah".
Cyril of
Jerusalem↗ (
Lecture 13, paragraph 27, at web address 1) apparently did not understand the reference and decided that "botsor" must mean a red garment:
"Again, when He had been judged before Pilate, He was clothed in red; for there they put on Him a purple robe. Is this also written? Esaias saith, 'Who is this that cometh from Edom? the redness of His garments is from Bosor' (מבצרה;
Isaiah lxiii. 1, 2.); who is this who in dishonor weareth purple? For Bosor has some such meaning in Hebrew. 'Why are Thy garments red, and Thy raiment as from a trodden wine-press?' But He answers and says, All day long have I stretched forth Mine hands unto a disobedient and gainsaying people."
For "scarlet" see LSJ s.v.
ko/kkos, II (literally the berry or gall of the
Quercus coccifera, used to dye this color; see e.g.
Pausanias 10.36.1-2).