hmm..that's extremely odd. I would say it's a block ID conflict, but blocks can't conflict..it's not even normally possible to remove these from the world. Can you cheat in any of the green sapphire tools?
Eloraam is doing some funky magic with overloading block IDs. The ore does not display in NEI because it does not exist as a separate item. There is only the general "gem ore" item, which is overloaded with all three gem types, the first being ruby ore. Which is why that one shows in NEI as occupying that block ID, when in fact it is only one of three.
Note that this is different from having different items told apart by damage values of the same block ID. The gem ores literally have exactly the same ID, down to exactly the same damage value. And yet they still generate properly in the world in separate deposits, do not stack with each other, drop different drops and participate in different recipes. I have never seen anything like it in other mods, and I have no idea how Eloraam did it, but gem ores aren't the only blocks she did it with.
Ok I can find Green Sapphire Ore in the terrain generation.
Thanks Omicron but one thing I don't understand is why can I see the blue Sapphire Ore then (as well as the Ruby Ore of course)?
Edit: In the creative thingy, I see that Ruby and blue Sapphire are classed in GregTech so maybe that's why. GreagTech has Ruby and (blue) Sapphire but no Green Sapphire. NEI shows 2 Ruby Ore so one must be GregTech and the other one must but all of RedPower combined ores as you said.
If you look up the recipe for for the gems to get the Ore's Item ID, you will see that the Item ID for Ruby Ore is 213, which shows, Green Sapphire Ore is 213:1 and Sapphire Ore is 213:2
If you look at the vanilla woods and the RP2 gems you will see the same thing, meaning the colon, : Though I'm not sure why the vanilla wood and gems show, but not the RP2 Ores. If you want to cheat the Ores in you are going to have to use the nether Ores and smelt them. Typing in 213:1 will not give you Green Sapphire Ore.