Śatapatha Brāhmaṇa ("of a hundred paths") 1.1.4.2

1.1.4.2

tasya yāni śuklāni ca kṛṣṇāni ca lomāni | tānyṛcāṃ ca sāmnāṃ ca rūpaṃ yāni śuklāni tāni sāmnāṃ rūpaṃ yāni kṛṣṇāni tānyṛcāṃ yadi vetarathā yānyeva kṛṣṇāni tāni sāmnāṃ rūpaṃ yāni śuklāni tānyṛcāṃ yānyeva babhrūṇīva harīṇi tāni yajuṣāṃ rūpam

Its white and black hairs represent the Rik-verses and the Sâman-verses; to wit, the white the Sâman and the black the Rik; or conversely, the black the Sâman and the white the Rik. The brown and the yellow ones, on the other hand, represent the Yagus-texts.