In the first scenes with The Mummy, he keeps changing color. When he first pops out of the sarcophagus, he's dark gray. Then, after Evylen finds the message on the sarcophagus lid, we see the mummy again and he is now brown. In the shot of Imhotep coming to life, he's light tan in color, and he goes back to gray in the scene where he's actually walking around.