ChU 6.4.4
यद् विद्युतो रोहितं रूपं तेजसस् तद् रूपम् । यच् छुक्लं तद् अपाम् । यत् कृष्णं तद् अन्नस्य । अपागाद् विद्युतो विद्युत्त्वम् । वाचारम्भणं विकारो नामधेयं त्रीणि रूपाणीत्य् एव सत्यम्
yad vidyuto rohitaṃ rūpaṃ tejasas tad rūpam | yac chuklaṃ tad apām | yat kṛṣṇaṃ tad annasya | apāgād vidyuto vidyuttvam | vācārambhaṇaṃ vikāro nāmadheyaṃ trīṇi rūpāṇīty eva satyam
Devanagari rendered by HREEM from the edition's roman (IAST) text; the IAST is the edition's own.
'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.
Translated by F. Max Müller