Your favicon is transparent. This is usually a good thing, but not for iOS Web Clips which are supposed to be opaque. Look at the sample on the left, this is how a user would see your favicon as a Web Clip on his device. What to do about this?

Your favicon is not transparent. This is a good thing for iOS Web Clips. Yet, web clip corners are rounded. Depending of your favicon, it may disrupt its design. For example, if your favicon features a square border, it will be cut at the corners. Look at the sample on the left and check how your favicon will be rendered on iOS. What do you want to do?

Use the original favicon as is. iOS will fill the transparent regions with black.