In the beginning of Part 2 (The Children), when we first see Leto, his eyes are completely normal. But when the camera turns back to him, his eyes have the bright blue tint from the spice. See more
I'm here, Father, as you knew I would be. We go forward; we go back. Don't be afraid. We're pre-born, my sister and I. Thanks to our mother and the spice... thanks to you! Yes, Father, it is me! Use my eyes, Father. Let me see for you.