[W]hile it would be easy to assume reference to skin colour, this would go against the spirit of the hymns: for Vedic poets, black always signifies e… - Michael Witzel

apart from archaeology, our principal source for the early period must be. the Rigveda…

Since the SarasvatI, which dries up progressively after the mid 2nd millennium BC is still described as a mighty river in the Rigveda, the earliest hymns in the latter must have been composed by C.1500 BC. (p. 98)

“[…] the Vedas were composed orally and they always were and still are, to some extent, oral literature. They must be regarded as tape recordings, made during the Vedic period and transmitted orally, and usually without the change of a single word.” (WITZEL 1997b:258).