it's called tempering. in order to make sure chocolate keeps its shiny gleen, you have to heat the melted mixture of mouthwatering miracles (see what I did there? alliteration. yes.) to a certain temperature, cool it down and then heat it again. if you fuck it up it will get those weird light brown spots on it when it cools. or, if you get it already done (wrapped, made, whatever) and it heats up and cools down, it will turn ugly, too.
why do i know that.