Hello there ^_^
When shiny pokemons evolve, they show as normal pokemons (on the evolution popup)
For example my shiny sandshrew evolved into a shiny sandslash (obviously) but when it showed me the popup for wether i wanted it to evolve or not, it looked while a normal sandshrew/sandslash.. after the evolution ofcourse, it became a beautiful shiny sandslash.
Thanks for your time :P