User blog comment:Martialmaniac/Sources external to the manga and Nen types/@comment-32818639-20190917190656/@comment-5780397-20190918024820

There are legitimate concerns about the reliability of that material, and, complaints aside, it is also worrisome that more than a few users assume that information from the guides actually comes from the manga/has the same degree of reliability. Isn't it also known that databooks and such are occasionally/often compiled by someone other than the author, whose name is then slapped on the cover?

As for eye and hair color, I think that in the majority of cases they are not sourced.