CHĀNDOGYA UPANISHAD · 6.4.6

यद् उ रोहितम् इवाभूद् इति तेजसस् तद् रूपम् इति तद् विदां चक्रुः ।
यद् उ शुक्लम् इवाभूद् इत्य् अपां रूपम् इति तद् विदां चक्रुः ।
यद् उ कृष्णम् इवाभूद् इत्य् अन्नस्य रूपम् इति तद् विदां चक्रुः ॥

yad u rohitam ivābhūd iti tejasas tad rūpam iti tad vidāṃ cakruḥ ।
yad u śuklam ivābhūd ity apāṃ rūpam iti tad vidāṃ cakruḥ ।
yad u kṛṣṇam ivābhūd ity annasya rūpam iti tad vidāṃ cakruḥ ॥

'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.

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