He is indeed great with colors and the lighting. You can really feel the forms, their anatomical shapes. I think you did a great study of his majestic piece! I know that the picture might be a little different from what it might be in real life, but if I have to compare yours to his piece, his is darker and less saturated. However, I can really see that you have captured his strong sense of anatomical forms with precise accuracy. So many details to take in account, I believe you have succeeded!
On term of the original piece being darker, let me give you example, compare his left hand. On the original one, it's so dark that you almost can't even see his fingers while on your piece, you can see them clearly with no problem. Maybe something to keep in mind since that's what gives the original one so rich of depth. That's definitely the art form of chiaroscuro. Rembrandt (one of my favorite artists) is also well known for this style. Notice both of their work is more to the dark side, not light side.
That's just me giving out my thoughts. I hope at least something of it will help you out. Either way, the most important part is that if you have learned something from it, then great job!