Our Master Amir Al-Mouminine (May His Glory be Mighty) said: "O Ṭāriq, the Imam is an angelic human, and a heavenly body."1
An angelic human and a heavenly body. Therefore, no obvious physical effect occurs. He is outside the limits of matter and outside the limits of time and space.
From him, he said in Al-Kashshī's book: Al-Faḍl ibn al-Ḥārith said: "I was in Sarr Man Ra'ā at the time of the departure of my Master Abū al-Ḥasan (May his glory be exalted). We saw Abū Muḥammad (May his glory be exalted) walking, with his clothes torn. I began to marvel at his majesty, his worthiness, the intensity of his color and his dark complexion, and I felt concern for him from fatigue. When night came, I saw him (May his glory be exalted) in my sleep, and he said: 'The color that you marveled at is a test from God for His creation, which He conducts as He wills, and that it is a change in the eyesight upon which no blame falls on the tested one. We are not like people, so we do not become fatigued as they do. We ask God for firmness and reflect upon God's creation, for there is room in it. And know that our speech in sleep is like our speech in wakefulness.'"2
This is important information, so pay attention... (The color that you marveled at is a test from God for His creation) This means that what you see is not the reality; rather, it is a test from God of the truth of your faith. Then he says, (and that it is a change in the eyesight), and this is what the Qur'ān indicated in the verse: (And We will turn their hearts and their eyes away, just as they refused to believe in it the first time)3
Meaning that the change is in your eye, not in the Master (May his glory be exalted).