Honest answer is - don't know where it is for sure. I have been to Seychelles but not to this place.
When it is artificially coloured, like a travel brochure and unless the photographer says exactly where,no one can be certain. There are many places in the Indian Ocean which look similar.
It could be La Digue as Sogo suggested but there are many Blue/Aquamarine coloured beaches in many countries.