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 "Vajradhara is the primordial buddha, the dharmakaya buddha. Vajradhara, depicted as dark blue in color, expresses the quintessence of buddhahood itself. Vajradhara represents the essence of the historical Buddha's realization of enlightenment."
"In Vajrayogini practice, we visualize our Guru as Buddha Vajradharma, who is the manifestation of the speech of all the Buddhas.
He has a red coloured body, one face, and two hands, which are crossed at his heart and hold a vajra and bell. He is the same nature as Conqueror Vajradhara and looks exactly like him, except that he is red and adorned with six bone ornaments, whereas Buddha Vajradhara is blue and wears jewelled ornaments."
Once I've read somewhere that Vajradharma is thought to be the Buddha of the Mother tantras; i cannot find this anymore though.