Xcode automatically added black default.png to my project . I didn't change it and I've sent it to the apple , it's waiting for review . Is it a rejection reason ? The default.png s can be just black or not ?
A black default image will not cause your app to be rejected. I have had apps accepted with no default image at all - if the app starts quickly enough, or there is no appropriate content for a launch image, then you don't need one.
Rant: Using the larger default image to indicate that an iPhone app works on the iPhone 5 is (IMO) a pretty poor decision - a key in the info plist would be much more sensible. As devices get faster, and resolution gets higher, launch images are becoming ridiculous. A universal app supporting iPhone 3, 4, 5, iPad and retina iPad will have megabytes of basically wasted space, to support an image that is shown for milliseconds. It was needed when devices were slower, but not really now.