IME Chromis nitida (Barrier Reef Chromis) & C. viridis (Green Chromis) will swim together, although they won't really "interact" with each other, but stick more to their own species groups. To minimise aggression (remember these are part of the damsel family) you would need a group of 5, or just a single fish.. Also as you said your damsel is electric blue/yellow, I am assuming you have one of the following... Fijian Damsel, Starck's Damsel or a male OTB. All three of these guys get relatively agro as they age (we had a large fijian in a display tank and it readily confronted a breeding pair of tomato clowns!). You best option IMO would be to go for a dottyback of sorts, and in aggreance with greeny the orchid would be high on my list =) or even a flasher or fairy wrasse. Or if you like something a bit different what about a Samurai Squirrelfish? Or a pair of clowns?