'indigo-related' originates from English, specifically the compound of 'indigo' and 'related', where 'indigo' derived from Latin 'indicum' (via Greek 'indikón' and Sanskrit 'nīla') meaning 'blue (from India)', and 'related' derived from Latin 'relatus' (from 'referre') meaning 'brought back / connected'.

'indigo' changed from Latin 'indicum' through Medieval Latin and Old French into modern English 'indigo'; 'related' changed from Latin 'relatus' via Old French and Middle English into the modern English adjective 'related', and the compound 'indigo-related' is formed in modern English by combining these elements.

Initially, 'indigo' meant 'blue (from India)' and 'related' meant 'brought back / connected', but combined in modern usage they denote something 'having a relation to indigo' (color, dye, or plant).