Wikipedia : This depiction of the Gathering of the Saints or the Gelupka linage is rarely seen out side of Tibet. In that respect it is unique.
This powerful presentation is of the refuge, or the gathering. Tsong Khapa is in the center with a medicine bowl. He is there to remove the 3 great poisons from your life: desire, hatred, & envy, in order to harmonize and reestablish the balance between the three humors: wind, bile, and phlegm. His iron bowl is filled with amrita, the divine healing nectar. He represents your local teacher or guru.
The gathering have been brought together on a lotus throne sitting upon a stupa that stands in the life-giving primal waters.
Tangkas with a black background like this one form a special category of contemplative paintings. They are a highly mystical and esoteric type, usually reserved for advanced practice. Black is the color of hate, transmuted by the alchemy of wisdom into the ultimate-reality-perfection wisdom. It is not that darkness is the absolute; the void is not nothingness. Darkness represents the imminence of the absolute, the threshold of experience. The absolute itself is rather the clear-light transparency within which all relative forms and vulnerable living things are sustained. But the dark connotes death, which enlightenment converts into the Body of Truth. It is used for terrific ritual actions, the radical conquest of evil in all its forms -- conquest not by annihilation, but by turning evil into good, the truth and basic operation of the mystical law.