Well normal is as normal does I think.
If you have 4 like that, plus now you've seen mine, probably it's not something out of the ordinary. Mine doesn't seem like he is sick, and the egg spots on the anal fin are nice and bright, so I don't think it is a symptom of anything.
When I look closely at mine, it seems like the blue is not just on the fins, the scales are actually blue also, but they are translucent, and in this case, I think the pink is in fact his flesh showing though or the color of the skin itself. I would guess that if the scales were translucent due to some sort of mineral deficiency, it would have corrected itself in my tank by now, unless it is a genetic deficiency like albinism.