this is a real challenge for underwater photography. you've got to get light on your subject. are you using a strobe? if not you need to get one (or two). then get really close to whatever it is you are trying to photography, because the strobes can only put light on stuff about 6 or 7 feet away from you.
as far as the green photos you already have, you could try color correcting them in a editing program like photoshop, lightroom, iphoto, aperture, etc.
you may also want to check the white balance setting on your camera. make sure the white balance setting is on auto unless you want (and know how) to do a custom white balance. if you figure out how to do that let me know.
the deeper you go the more critical all this becomes. for example, all the red light is filtered out by the water after only 12 feet or so. so when you're at 80+ feet everything becomes monochromatic, and thus the need to put light on it.
hope this helps.