The first member of a tat-puruṣa samāsa preserves its original accent when a word denoting colour is compounded with another colour denoting word but not so when it is the word eta,
Thus कृष्ण꣡सारङ्गी, लो꣡हितसारङ्गी, कृष्ण꣡कल्माषः, लो꣡हितकल्माषः ॥ कृष्ण is formed by मक् affix (Unadi. III. 4) and has acute on the final 3.1.3. लोहित is formed by the affix तन् added to रुह् (Unadi, III. 94) and has accent on the first 6.1.197.
Why do we say 'color-denoting word'? Observe परमकृष्णः꣡ 6.1.223. Why do we say 'with another color denoting word'? Observe कृष्णतिलाः꣡ 6.1.223. Why do we say 'but not when it is एत'? Observe कृष्णेतः꣡, लोहितैतः꣡ ॥ The compounding takes place by 2.1.69.,