Shatapatha Brahmana 14.1.3.29

14.1.3.29

atha suvarṇaṃ hiraṇyamupariṣṭānnidadhāti divaḥ saṃspṛśaspāhītyetadvai devā abibhayuryadvai na imamupariṣṭādrakṣāṃsi nāṣṭrā na hanyurityagnervā etadreto yaddhiraṇyaṃ nāṣṭrāṇāṃ rakṣasāmapahatyā atho dyaurha vā etasmādbibhayāṃ cakāra yadvai māyaṃ taptaḥ śuśucāno na hiṃsyāditi tadevāsyā etadantardadhāti haritam bhavati hariṇīva hi dyauḥ

He then places a gold plate (weighing a hundred grains) on the top (of the pot), with, 'Protect it from contact with the sky!' For at that time the gods were afraid lest the Rakshas, the fiends, might injure that (Pravargya) of theirs from above; and that--to wit, gold--being Agni's seed, it (serves) for repelling the fiends, the Rakshas. But, indeed, the Sky also was afraid of this lest this (Pravargya), when heated and glowing, might injure it: he thus keeps it separate therefrom. It is yellow, for yellow, as it were, is the sky.