If it were me I would probably just have a shared wardrobe of clothes whilst they were newborns. There may be some outfits the same in there, which I may or may not choose to dress them in at the same time, but there may also be 'one off' outfits too. For me, in that newborn craziness stage, just being able to pick up anything and put it on the baby without wondering who's it is would be easier for me. I think that as they got older and weren't going through as many outfits, I would probably start buying them their 'own' outfits. That being said, I can see how colour coding their outfits could make telling them apart much easier so I can see why you're thinking of doing it!