Jack the Ripper: I shall tell you where we are. We're in the darkest region of the human brain, a radiant abyss where men go to find themselves.
Netley: I don't understand, sir.
Jack the Ripper: Hell, Netley. We are in hell.
Sir William Gull: No man amongst you is fit to judge the mighty art that I have wrought. Your rituals are empty oaths you neither understand, nor live by. The Great Architect speaks to me. He is the balance where my deeds are weighed and judged, not you.
Sir William Gull: One day men will look back and say that I gave birth to the Twentieth century.
Answer: His eyes are not just darker, his entire eyes are completely black. This was done by CGI effects to show that the murderous Ripper side to Gull's persona is taking over and is in control.
Twotall