Personally, I have eyes that are brown on the interior of the iris close to the pupil, and blue/green on the exterior. I too have noticed the coloration of my eyes changing, however in my case the brown ring will recede and the bands of blue/green will expand. What I would recommend if you are serious in monitoring the shift of your eye color is to keep a journal and track various inputs that you believe may influence eye color. Then, you can begin experimenting with various factors and see how they influence your eyes.
In the last year or so I have transitioned my diet from staples of red meat / veggies / starches / fermented dairy to rice / dairy / eggs. I have also started to fairly regularly supplement with aspirin/K2 on top of my habitual high doses of vitamin D supplementation (I live in a place with relatively long harsh winters). The things I find the most influential on my eyes are: eating gummy bears, drinking milk, and exposure to sunlight, but not necessarily in that order. Like @Adolf_Hitler said, I think that there is a lot to the common saying "The eyes are the window to the soul". Ultimately, I see my iris coloration as the manifestation of internal conflict and seek to tame my nature and structure it towards a higher ordered state of living.
Hope you found this helpful!