What is the name of A fruitcake often coloured with saffron and covered with marzipan traditionally eaten at Easter?

It is called a Simnel Cake. The name is a mystery but may mean that it was originally made with semolina flour. Originally the cake was made for Mothering Sunday, not Easter, by the way, and would be given to mothers by daughters.

There are normally eleven marzipan balls on top of the cake; these represent Jesus' disciples, of whom there were twelve but treacherous Judas is excluded leaving eleven.

Hope this helps.