Have you spoken to the mother? Are you sure you are suppose to purchase it? I bought my child's dress and so did everyone else I know. Of the three you posted I like the 3rd. I do believe it is suppose to be all white or off white.

I like the number one
But look at this:
http://uk.monsoon.co.uk/uk/children/christening

I would definitely go for all white. Why not take a look at m&s as I know they do some pretty ones.
http://www.marksandspencer.com/l/kids/collections-and-trends/christening-and-communion?&mcptredirect&edcredirect

Hello! I was asked to be a God mother for a doughter of my friend and in their traditions god mother should buy a christening dress. I found an obline shop with cute and affordable dresses, but am not sure about which one to choose. What would be your choice?
1. https://three-snails.com/collections/baptism-clothes/products/girls-dress-angel-day
2. https://three-snails.com/collections/dresses-1/products/handmade-crocheted-dress-princess-2
3. https://three-snails.com/collections/baptism-clothes/products/baptism-outfits-for-girl-christening

And should it be totally white?