It may be due to moulting. But mine started to reduce problem in addition to the yellow colour in its eye patch. Just after a little bit of experimenting we uncovered that Placing his cage outdoors most days for a minimum of twenty minutes inside the Solar sorted this out. https://hill-mynah-birds-for-sale32210.webbuzzfeed.com/28386554/how-mynah-for-sale-uk-can-save-you-time-stress-and-money