Make an icon in Photoshop, Gimp or whatever (use transparent background and save as PNG), edit folder properties and use this PNG file as icon (download if to phone first of course). I'm not sure how does it work in Apex but in Nova it's pretty simple.
Somehow my GT-i9505 sent this...
Samsung Galaxy S4 GT-i9505
Rooted, deodexed, stock + 3Minit Framework