Thank you @danilo_tedde for the feedback! In regards to adding some more hue variation in other places of the piece, I often tend to purposely negate some detail on areas where I don't want to emphasize that much attention. Though you're 100% right about it and it's something I should consider adding especially when it's just done for the study.
In regards to the eye, I'm not really sure so I'll send the reference photo for better comparison. Also that's a very helpful trick, thanks!
Lastly, as always, thank you @Lockenheim for being very active on pretty much everyone's progress! I cannot emphasize enough how your comments are helping me to push myself further when it comes to my studies. Also, I would like to apologize for the lack of involvement in your or other people's work, I'm not really that great nor confident when it comes to giving advice/feedback. Though it's something that I would try to work on in the near future.