Firstly understanding "Black Rosy Adenium" It is not a true BLACK rosy adenium. Almost they are deep dark red or deep dark purple. As we have seen the actual flower bloom in Thailand almost it has black inner petal layer and very deep strong red/purple in outer petal layers. So some Thai gardener call "Black Adenium". Do not too worried Time will tell for you accurate adenium flower colors.
Anyway please mind that strong high sun, high heat growing conditions is required for growing these plants for a good flower display. Bright light, partial shade or no sun is not good for almost black adenium.