Brihat Samhita
निशि सुरचापं सितवर्णाद्यं जनयति पीडां द्विजपूर्वाणाम् । भवति च यस्यां दिशि तद्देश्यं नरपतिमुख्यं नचिराद्धन्यात् ॥ ३५-०८ ॥
If, at night, the rainbow should appear white, red, yellow or black, the Brāhmaṇas, the Kṣatriyas, the Vaiśyas and the Śūdras will suffer respectively. If at night the rainbow should appear in particular quarters of the sky, the rulers in those quarters of the Earth will perish.
english translation
nizi suracApaM sitavarNAdyaM janayati pIDAM dvijapUrvANAm । bhavati ca yasyAM dizi taddezyaM narapatimukhyaM nacirAddhanyAt ॥ 35-08 ॥
hk transliteration by Sanscript