Valmiki Ramayan in Aryakanda describes Ma Sita’s beauty, her complexion and skin colour
Surpankha describes Ma Sita to her brother Ravan
in Sarga 34
रामस्य तु विशालाक्षी पूर्णेन्दु सदृश आनना |
धर्म पत्नी प्रिया नित्यम् भर्तृः प्रिय हिते रता || ३-३४-१५
"But, one with her broad-eyes, face similar to the full-moon is the dear and wedded wife of Rama, and she always takes delight in the well-being of her dear one, namely Ram.
सा सुकेशी सुनासोरुः सुरूपा च यशस्विनी |
देवत इव वनस्थ अस्यराजते श्रीर् इव अपरा || ३-३४-१६
"She is the one with lengthy hairdo, her nose and thighs are fine, and that glorious one with fine looks is the wife of Rama, and she is beaming forth like a sylvan deity situated in that woodland, who in turn is like Goddess Lakshmi in a temporal form.
तप्त कांचन वर्ण आभा रक्त तुंग नखी शुभा |
सीता नाम वरारोहा वैदेही तनु मध्यमा || ३-३४-१७
"She has a complexion matching the shade of refined gold, her nails are rosy and jutting, and she with her curvaceous hips and slim waist is the daughter of King of Videha, and known as Sita”.
न एव देवी न गंधर्वा न यक्षी न च किंनरी |
तथा रूपा मया नारी दृष्ट पूर्वा महीतले || ३-३४-१८
"So far I have not seen any Goddess with such a comeliness; a Gandharva female - no; a Yaksha female - no; a Kinnara female - no; and a woman, no, not on the face of earth!
Gandharvas are celestial beings
Yakshas are supernatural beings
Kinnara are part human, part birds and look after the well beings of humans.
Surpankha says to Ravan that she has not seen any Goddess or anyone one from Gandharva, Yaksha , Kinnara or any woman on the face of the Earth as beautiful as Ma Sita.
Mata Sita is described as having complexion matching the shade of refined gold ( usually glowing too).