Why are my healthy parrot's feathers changing color? Is it molting?

As far as I can see from the photo, the feathers look normal and healthy. Some color change and darkening of feathers is normal, and the feathers may continue to change somewhat until Pa Pa reaches maturity. Molts can also change feather color some as old feathers fall out and new ones come in. If he is otherwise healthy, normal, and active, I wouldn't be worried. If the feathers change rapidly, fall out, seem bothersome, or you notice any signs of illness in addition to the changes, scheduling a checkup with your local vet to rule out any health issues is always the best course of action.

Stress and diet can both contribute to feather health and coloring. As long as your bird is behaving normally otherwise, there is likely no cause for concern. Monitor for lethargy, loss of appetite, loose droppings or excessive feather loss (not due to molting). These are symptoms that should be addressed by your veterinarian or an experienced avian veterinarian.

Feather changes can be for a number of reasons including normal molting, aging to adulthood, parasites, skin issues and nutrient problems. If Rangu is acting ill at all (not eating or drinking, sleeping a lot, losing feathers, etc) scheduling a vet checkup to look for any potential issues is best.

Feather loss can be from any number of things, so finding the underlying cause is best. Molting is a normal loss of feathers that occurs 1-2 times a year and all the old feathers are replaced with new ones. You will see "pin" feathers appearing on the skin (look like needles or pins) to indicate this is a molt and new feathers are growing in. Making sure Mithu is on a balanced diet can help ensure he grows in new feathers. Skin issues such as parasites, infections, nutritional issues, etc can also cause feathers to fall out. Treating any visible wounds, making sure Mithu is on a balanced diet, and using a mite spray to treat any external parasites can help. Illness can sometimes cause feathers to fall out either due to a lack of nutrition or from the illness itself. If you can't find an immediate problem, having a vet examine Mithu is best to rule out any illness. Boredom and stress can also cause feather plucking, which may make it look like the feathers are falling out. Making sure your bird is kept in a quiet, stress-free area away from noisy pets and people, and providing lots of enrichment such as toys to play with and chew on, fun treats, and time spend together can help. In some cases, an Elizabethan (e-collar) may be needed to break the behavior if it has become a habit.

It looks like he may be losing some downy feathers, which can happen during a molt or when adult feathers are coming in on younger birds. If it's a molt, you'll see new feathers growing in that look like little pins/needles poking out of the skin (hence the name pin feather) -- though these are usually better visible for large feathers such as tail/wing. If you're not seeing this, he seems to be picking at his belly a lot, or you see issues such as red skin, parasites on the skin, etc, a vet visit is a good idea to rule out any health issues.

If he is not picking out his feathers, he is likely molting: Molt is a very strenuous time for a bird as almost all its energy is used to making new feathers. It takes seven to ten days for a feather to begin to emerge after one was shed and then this new feather takes up to 8 weeks to fully develop. During molting your bird will be cranky, nap more often and it is especially necessary at this time to feed them a very healthy diet and keep a close eye on them as they will be using lots of their nutrients to grow and replace the feathers. Feed lots of greens such as kale (extra calcium) and you can feed mashed up hard-boiled egg and also offer some boiled chicken. Both of these are high sources of protein for making new feathers.

Harry could be molting, which is a normal thing that occurs about once or twice a year. This is when your bird loses their feathers and then replaces them with new ones. You can check if this is the case by looking for "pin" feathers, or what looks like little pins growing out of the skin (these are the new feathers coming in). Other things to look for include making sure Harry is on a balanced diet, and checking for mites or other skin issues that can also cause feather loss.