तेन रक्तं रागात्

The verb रञ्ज् means to change white into another color. That by which a thing is coloured is called रागः 'color'. तेन 'by which', i.e. after a word in the instrumental case in construction, being the name of a particular colour. Thus कषायेण रक्तं वस्त्रं = काषायम् 'a cloth coloured of a dull red'. So also मांजिष्ठम्, कौसुम्भम् ॥

Why do we say रागात् \after the name of a color\? Observe देवदत्तेन रक्तं वस्त्रम्, here the affix अण् will not come after the word 'Devadattena', for though it is in construction in the instrumental case, yet it is not the name of a colour.

In the sentence \काषायौ गर्दभस्य कर्णौ, हारिद्रौ कुक्कटस्यादौ\ the words काषाय and हारिद्र are used metaphorically.

From this sutra up to 4.2.12 inclusive, the affixes are to be added to the word which is in the instrumental case in construction in a sentence 4.1.82: as in the last chapter, the affixes were added to a word in the genitive case.,