शुद्धस्यैको हारिद्रस्य सुवर्णो वर्णकः ॥ कZ_०२.१३.१५ ॥
śuddhasyaiko hāridrasya suvarṇo varṇakaḥ
For the purified (metal), a single (standard) ‘hāridra’ coloring is used; gold is the color-reference/finishing agent.
Uniform finish aids public trust and official verification, and reduces the circulation of visually deceptive, adulterated metal.