There are NO dumb questions... but there can be dumb answers
When you say the 'part around the eyes' are you referring to the orbital ring (the naked skin ring around the eyes) or the colored feathers ring around the orbital ring? In any case, the orbital ring does not change color because it's skin (unless we are talking a bruise or something like that). The colored feathers ring should not change color either. It might look a bit like a 'broken line' (meaning, empty spaces between colored feathers) when the bird is molting but these feathers are so small, I doubt the 'hole' made by the old feather falling off is noticeable. Now, usually, when you see grey on a bird that does not have a grey plumage, what you are seeing is the down feathers. Down are the small, very fluffy feathers that are under the contour feathers (the roundish ones that cover the bird's body) and which provide insulation.
A healthy endocrine system means one that is working as nature meant for it to work. The endocrine system is the one that governs glands and their production of hormones and, in birds, it's regulated by the length of daylight. The days are not always of the same length during the year, we have long days in the summer and short days in the winter and the difference in the number of hours that there is light is what tells the bird's glands when to start producing hormones and when to stop. And the quality of light is what makes it produce other hormones (like the ones that are called "reward hormone' or 'happiness hormone'). Birds are the most depedent species of all the vertebrates to quality and duration of light - to them, light is almost a nutrient. Now, although we, birdkeepers, usually refer to the endocrine system to explain sexual hormone production, in reality, it is much more complex than that because it regulates sleep, appetite, mood, cell regeneration, etc. - even the immune system! And that's why it's imperative that their endocrine system is healthy and in good working order. How do we keep it that way? By keeping the bird at a strict solar schedule with full exposure to dawn and dusk. Why do we need to do this? Because their 'internal clock' (the one that tells the bird's body when it's time to eat, to sleep, to molt, to breed, etc) is turn on by the light of dawn and off with the light of dusk. Nature never meant for birds to live indoors, she made them to live outdoors and exposed to the sun light and the different seasons.