When you say "sporadically", is this occurring while you are at home and supervising? Or are you noticing this discolouration when you get home after being out? Does his plumage return to normal in between times? Is there any odour associated with it or change in demeanour or behaviour?
I work from home. Is just getting darker the feathers. Sporadically as I noticed weeks ago it was getting darker and darker. There is no odor. Behavior is the same, I feed him walnuts and his seeds. His cage is always open. Is he molting? Or is he sick? I’m sorry not sure what to do
To be perfectly honest it's difficult to say, and unfortunately we are not avian medical professionals here. I was initially thinking maybe he is dunking himself in his drinking water while you're not looking, but in that case of course the feathers would return to normal colouration. Sometimes discolouration like this can be caused by oils from our hands but this colour change does look somewhat more dramatic. Has he had a check up by a CAV (Certified Avian Vet)?
I am not personally aware if Indian Ringnecks are banned there. The following link may help you to find a local avian vet - they should know what local regulations exist and will be able to advise you if treatment is available...
My First question would be if this is right after a bath... My IRN always looked similar like this after a bath, but once dry he looked normal. Does the bird look like this all the time and always, or just sometimes? If it's all the time, then an avian vet would be a must. However, I really don't have any suggestions if the species is banned where you live..