I had/have under similar light (18W 50-50 PC in Nano-cube 6g): branching hammers and frogspawn, neon-green candycane, white xenia, hairy mushroom (Rhodactis), white lemnalia, and non-photosynthetic corals (feeding makes necessary massive water changes) - red finger gorgonian (Diodogorgia), sun coral, scleronephtya, purple lemnalia. Not all in the same time.
Not enough light for: bright red mushrooms (if they are at the bottom, while rhodactis is perfectly OK), green star polyps, kenya tree (capnella), anthelia, yellow polyps.
But: corals at the top of the tank, with the very small water layer between them and the light (say, 2"), will have more than enough light. Don't forget about colorful invertebrates, other than corals, like shrimp, stars, or pink-green or yellow cucumbers (beware).
Fish: clowns may attack them (mine did), but crorimises are making the tank look alive and very marine color, mermaid-like.