Greek myth does not give Hecate a eye color.
blue
Athena, the Greek goddess of wisdom, had gray eyes.
The goddess Athena was said to have gray eyes.
Persephone, being a Greek goddess, may change her appearance (thus eye color) at will.
Hestia the greek goddess of hearth and fire and family has the color brownish eyes
Athena had gray eyes.
Persephone, being a goddess, could change the color of her eyes at will.
Athena (Greek mythology)
Persephone, being a goddess, could change the color of her eyes at will.
Hestia the Greek goddess of the hearth, is known to have brown eyes like fire wood or orange flames as her eyes. Not an evil flame like ares but a warm, fuzzy fire for cold winter nights. That is what is known for Hestia's eyes
I believe that they are either green or brown
Persephone, being a goddess of Greek myth, could change her appearance and form (thus eyes) at will.
Aqua (changing from Blue to Green) seems most likely to me because her parents were of the sea ...