Try any type of sponge for your idol, pick a few up at your LFS, place them around the tank and let the idol pick at them. You can also try angel formula which has sponge in it.
Try chopped raw shrimp, squid, octo, Spectrum pellets and so on, pick up some macro algae for green.
Idols are non stop swimmers day & night, and they will graze day and night, I would recommend feeding this idol 3-4 times per day, or they can starve, which is not uncommon for this fish.
Feed this fish often and keeping trying to add a variety of foods, try feeding when the lights are out also.
If you are unable to get this idol on different foods take a turkey baster and try placing the different foods in a clam shell, see if it will nibble that way.
Hope this helps
Kaye