premise: European sailors, for whom the temple was an importa nt landmark, enabling them to keep out of the dangerous shallows of the Orissa coast (they nearly had it turned into a lighthouse), called it the Black Pagoda in order to be able to distinguish it from the White Pagoda of Puri's whitewashed Jaggannath Temple further down the coast.
hypothesis: The temple was called the Black Pagoda to distinguish it.