Why some icons & splash contains alpha channel

Merry Xmas, dear ionic community.
I generated a project by:
ionic start testpj blank --type=ionic1
then I copied my icon.png and splash.png which both contains no alpha channels.
then I run:
ionic cordova resources. IOS and Android icons and splashes generated as expected but when I examine the files, some of them contains alpha channel.

I read that apple doensn’t accept icons&splash with alpha channels. Is that true?
Why ionic cordova resources bring the alpha channels back and only to some icons&splashes?
Please help me