Question about transfers that I'm struggling to find in the libers and black books

Is there some kind of difference between icons that are filled or not filled out, or is it just an aesthetic thing mostly that doesn't have lore implications?
Also is it more common to have coherent iconography across a squad (all marines have their icon on their shoulder or the same colour etc.) or would it be more "realistic" for there to be a mix of iconography that still technically communicates the same information (some marines have their role icon on their shoulder while some have it on their kneepad, some have it in a white colour while some have it black etc.)