I can't see your picture so I've linked to one I found. They seem to like dancing.

http://www.duskyswondersite.com/animals/blue-footed-booby/

What a wonderful-looking creature. I've not come across them before. I was going to say that perhaps they don't know they have blue feet themselves and that's why they like them in their partner, but I reckon they can see their own feet very well.

Don't go thinking that, just because males and females sport the colourful flippers, they cannot therefore be to attract mates. It's quite possible that the bluer the colour, the better the owner is at foraging for food. In European tits (I think it was the great tit Parus major) it has been shown that extra-yellow feathers are a result of a healthy diet of grubs. Blue tits wear a blue crown of feathers which looks more blue and more tidy when the owner gets plenty of food. A bird that can collect more food is likely to be a better parent for its children.

Songbirds sing even when they don't necessarily need to defend territory. This is thought, by some, to show other birds that the singer has time to sing, "Look at me, I'm beautiful, I can sing for ages and I still have time to feed myself and my kids".

Sexual selection in evolution, can be a runaway thing too. Look at birds of paradise. It's not hard to imagine that a little bit of blueness in the legs attracted a mate who liked blue legs. The offspring might have had a tendency to like blue legs and to have blue legs (maybe both at once). If other families admired the blue legs, it wouldn't be long before everyone wanted them.

i think they cannot survive without thier feet (cannot fly, cannot swim), so the feet evolved to be blue.  WHY?  because on the island where they lived for many eons (lets call it "boobie paradise isle"), there was a poison flower whose color was blue.  every animal stayed away from it, and the boobys whose feet were that color didnt get thier feet pecked on by other meaner birds. the bluer the better.  the white feet were pecked upon and didnt make it.  what do you think?  my hubby says the blue feet are a result of what they eat, like blue shelled crabs.  i like my reason better...............