I furthermore suggest that Discourse should display the “apple touch icon” in Settings with a black background, to make it more obvious to site administrators what will happen if they try to use a transparent icon as the “apple touch icon.”
EDIT: It would be even better if the admin Settings would display “apple touch icon” with rounded corners and a black background, so site administrators could see that the image will have an Apple-provided border radius. Another forum I’m on had an “apple touch icon” with a colored border, and of course it looked terrible when Apple added rounded corners…