The five Tathagata [or also: »Dhyani«] Buddhas are the white Vairocana, the blue Akshobhya, the yellow Ratnasambhava, the red Amitâbha and the green Amoghasiddhi.
They are not historical Buddhas. These Buddhas are visualized in the course of a meditation.
Each of the five Tathagata Buddhas is associated with certain symbols, characteristics and cardinal points and embody one of five wisdoms.
By associating the Buddhas with the five cardinal directions [The center is considered the 5th cardinal direction] they are rulers of the five cosmic realms of »ether, water, earth, fire and air«.
Source: Wisdom and Compassion - The Sacred Art of Tibet
Akshobhya Literally, Unshakable, he is the lord of the Vajra clan and occupies the eastern direction in many popular tantras, or the center in the advanced Unexcelled Yoga tantras [switching with Vairochana]. Akshobhya represents the transrautation of delusion [or hate into mirror wisdom or reality wisdom], and the purity of the aggregate, his color is white [or blue].
Amitabha Literally, Infinite Light, he is the Transcendent Buddha of the west, and lord of the Lotos family. He represents the transmutation of lust into discriminating wisdom, and the purity of the conceptual aggregate. His color is ruby. Associated with the Buddha Amitayus [Infinite Life] and the Bodhisattva Avalokiteshvara, he is widely known outside of tantric Buddhism as the Buddha of the Blissful Pure Land in the west [Sukhavati], and is the object of devotion of the numerous Pure Land believers throughout Asia.
Amoghasiddhi Literally, Unfailingly Accomplished, he is the Transcendent Buddha of the north, and lord of the Action clan. He represents the transmutation of envy into all-accomplishing wisdom, and the purity of the performance aggregate. His color is emerald.
Ratnasambhava Literally, Buddha of Precious Birth, he is the Transcendent Buddha of the southern direction and Lord of the Jewel clan. He represents the transmutation of pride and stinginess into the equality wisdom, and the purification of the aggregate of Sensation. His color is gold.
Vairochana Literally, Shining One, he is one of the Five Transcendent [Tathagata] Buddhas. He is the lord of the Buddha clan and occupies the center in many popular tantras and the eastern direction in the advanced Unexcelled Yoga tantras [switching places with Akshobhya]. Vairochana represents the transmutation of hate [or delusion] into perfect reality, or mirrorlike, wisdom, and the purity of the consciousness [or form] aggregate. His color is blue [or white].
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