the title refers to something a friend of mine had mentioned before.
XD research time..hehe
Maybe "grayman" refers to a Noah (err...gray-skinned Noah?)
and "D." is just wel..
kewl..
Nothing can really feel like they should change the title after you've seen the series, but if you never saw or heard of it before it wouldn't really sound interesting..........so how about The innocense of life or maye Noah's ark of Darkness
Why do you want to call it Innocence? None of the options fits at all. D.Gray-Man is good enough and I really like it. My opinion of course. After all we have our own tastes.
Maybe this image from the manga can help why the author wanted to name it D.Gray-Man. I have it in box where the author talks about it.