There is only one kind of reef/fish safe paint 2 part epoxy NSF-61 certified for potable water, any other paint that comes in contact with the saltwater will leach very bad chemicals into the water and very quickly kill any and probably all inhabitants of the tank. I'm not sure how you're planning on mounting your return but please make sure the paint is not immersed or placed in such a way as to allow any evaporation condensation to drip back into the tank.
The black pvc pipe sold in the home improvement stores is not certified safe for potable water either, it's intended for use as waste lines only. You can find black "reef safe" flexible pvc pipe from several online sources if you must have black and can't afford the *ridiculous* price of the 2-part epoxy paint.
Just my research over the last year so I could be badly mistaken, Lord knows it wouldn't be the first time. I'm sure one of the sharks will jump in to correct me if I'm wrong.
Good luck and, by the way, the bar does look very professionally done!
Later,
Paul