Khandogya-Upanishad: Sixth Prapathaka, Fourth Khanda

2. “The red colour of the sun (aditya) is the colour of fire, the white of water, the black of earth. Thus vanishes what we call the sun, as a mere variety, being a name, arising from speech. What is true are the three colours.

3. “The red colour of the moon is the colour of fire, the white of water, the black of earth. Thus vanishes what we call the moon, as a mere variety, being a name, arising from speech. What is true are the three colours.

4. “The red colour of the lightning is the colour of fire, the white of water, the black of earth. Thus vanishes what we call the lightning, as a mere variety, being a name, arising from speech. What is true are the three colours.

5. “Great householders and great theologians of olden times who knew this, have declared the same, saying, ‘No one can henceforth mention to us anything which we have not heard, perceived, or known.’ Out of these (three colours or forms) they knew all.

6. “Whatever they thought looked red, they knew was the colour of fire. Whatever they thought looked white, they knew was the colour of water. Whatever they thought looked black, they knew was the colour of earth.

7. “Whatever they thought was altogether unknown, they knew was some combination of those three beings (devata).

“Now learn from me, my friend, how those three beings, when they reach man, become each of them tripartite.