B Vitamins
Most seed-based diets are deficient in vitamin B. If your bird lacks any of the family of B-vitamins he may exhibit poor skin and feather quality. A deficiency in the B-vitamin riboflavin has been associated with abnormal yellow coloring. Normally, B-vitamins are produced in your bird's gut. If he isn't getting the nutrition he needs to generate these vitamins for himself, you can add some boiled egg to his diet. Most good sources of B-vitamins are animal-based; egg is the most suitable source that his digestive system can handle.