they're (it's) the same word:

sorrel, n. and adj.
("sQr@l) Forms: (arch.) sorel, sorelle, sowrell, sorell, soril; sorrell, -ill, sorrel. [a. OF. sorel (soreal, -eaul, -iel), f. sore sore

adj. Of a bright chestnut colour; reddish brown: a. Of horses (or other animals).
b. Of hair or persons.
c. Of colour or hue.
d. Comb., as sorrel-coloured adj.; sorrel-top colloq. (orig. U.S.), a red-haired person.

n.
1. a. A horse of a bright chestnut or reddish brown colour; also as the name of a horse. (So OF. Sorel.)
b. In allusive use

2. A buck in its third year. Now Obs. or arch.
1486 Bk. St. Albans, Hunting eiv, And ye speke of the Bucke, the fyrst yere he is A fawne,+The secunde yere a preket, the iii. yere a sowrell. 1588 Shakes. L.L.L. iv. ii. 60 The Dogges did yell,+then Sorell iumps from thicket.

3. A sorrel or reddish-brown colour. Freq. with reference to horses.