The reason it was called Blue Harvest is it was a fake title actually used during filming revenge aka return of the jedi.

They pretended they were shooting a low budget horror picture called BLUE HARVEST: Horror Beyond Imagination.

Ironically enough an episode of the ewoks cartoon was also called blue harvest.

It was also a pretty elaborate was to trick people as they even had call sheets with fake names for the actors.

Until people found out that they were filming a star wars movie which just happened to be a sequel to empire strikes back one of the most sucessful films in film history at that point in time.