Atharvavedaparishishta 70.10.2

70.10.2

viprāṇāṃ bhavati hi śuklam ambudoṣe rājānaṃ sapadi nihanti lohitaṃ ca | pītaṃ ced bhavati nihanti vaiśyavargaṃ śūdrāṇāṃ bhavati hi kṛṣṇapiṅgadoṣe ||

For if [the liquid] is white in an affliction of water, it belongs to Brahmins; and if red, it strikes the king at once; / if it is yellow, it strikes the Vaiśya caste; and if it has a blackish-yellow affliction, it belongs to the Śūdras.