What i did with my "taiaha" is i contacted the museum of tepapa nz
here (link) And i got an honest reply back from them, very nice people you should really send them a message!
Also you can check out there online collection
here (link)
Or if you want to see them all on one page (like i do) use
this link
Also i get what youre saying about color, very hard, i guess it depends on storage condition and age and also how long was it in use by the natives?