"He is not great and He is not small. He is the greatest and He is the smallest. He has no color. His color is dark and the corners of His eyes are red.
And Bhaktiratnakara gives the following description of Lord Rama:
"All glories to him whose complexion is the color of greeen grass mixed with the new born cloud of the rainy season, and whose eyes are as black as collyrium. He remains peaceful during battles wearing his arrows on his right shoulder and his bow on the left.
But both Krishna karnamrita and Bhaktiratnakara are strictly speaking vaisnava kavya, not sastra (eg not sruti or smrti, not even tantra, tikas or tippanies). I can not find actual references in sastras as to the color of Krsna's eyes, not to speak of Radha's eyes.