Sâ is the white light of the sun, ama the blue exceeding darkness, and that makes Sâma. Now that golden person, who is seen within the sun, with golden beard and golden hair, golden altogether to the very tips of his nails,

In plain words: Sa is the sun's white light and ama is its dark blue, and together they make Sama. Then the text begins describing a golden person seen inside the sun, golden from his beard and hair down to his fingernails.