It could indeed be dirty ivory, but the grey-ish areas of the hilt suggest bone to me. These areas would be some of the outer grain of the spongiose core tissue. Ivory is much more solid and usually whiter and the material has a more 'live' glow. Hard to explain, but a focused picture of the handle surface should be able to decide it.
Very cool little knife in all regards. I've never personally seen a gunong in hand, so I am also surprised by the size. I like it even better now that I know that it is so small - such a great little stabber!
Thanks for sharing!
Best wishes, - Thor