From an unused root meaning to be warm, i.e. (by implication) sunburnt or swarthy (blackish) -- brown.
H2345. chum
חוּם adjective darkened, dark brown or black, only of colour of sheep (in Genesis 30, J); — בכשׂבים וכלשֶֿׂהחֿוּם Genesis 30:32, בכ ׳וְחוּם 30:33, 35, בְּצאֹן וכלחֿוּם 30:40 (clause probably interpolated Ol Hup De We Di).
חוֺמָה see below חמה.