CHĀNDOGYA UPANISHAD · 6.4.1

यद् अग्ने रोहितं रूपं तेजसस् तद् रूपम् ।
यच् छुक्लं तद् अपाम् ।
यत् कृष्णं तद् अन्नस्य ।
अपागाद् अग्नेर् अग्नित्वम् ।
वाचारम्भणं विकारो नामधेयं त्रीणि रूपाणीत्य् एव सत्यम् ॥

yad agne rohitaṃ rūpaṃ tejasas tad rūpam ।
yac chuklaṃ tad apām ।
yat kṛṣṇaṃ tad annasya ।
apāgād agner agnitvam ।
vācārambhaṇaṃ vikāro nāmadheyaṃ trīṇi rūpāṇīty eva satyam ॥

'The red colour of burning fire (agni) is the colour of fire, the white colour of fire is the colour of water, the black colour of fire the colour of earth. Thus vanishes what we call fire, as a mere variety, being a name, arising from speech. What is true (satya) are the three colours (or forms).

F. Max Müller · The Upanishads, Sacred Books of the East 1 (1879)