Many achronim write about a woman who wants to make a shaitel out of her own hair – i believe this is very relevant, because it speaks to the material used, not the method of attachment and the appearance thereof after the shaitel is made. Using realistic looking material has a basis, but making it such that the woman herself appears to be shaitel-less, seems to involve several issues: maaris ayin, and the inability to distinguish one’s self as a married woman, and I’m sure there’s more. Also of note is Avi’s mentioning of rav moshe’s psak regarding divorcing a woman who does not cover her hair. When I learned the sugya in kesuvos I hit on a chidush based on rashi and other rishonim that we don’t find that one must divorce his wife for other iniquities; only in regard to tznius issues that are in the public eye. The reason is, I believe, because the way a wife behaves in public is a reflection on the husband, since it is assumed that had he wanted to, he could have forced her to dress differently. Since most women did not cover their hair in Europe (and america for many years) it had bo reflection on the husband, so there was no need to divorce her.
That being said, I think if a woman appears to not be wearing a shaitel, it would be in that category even if she technically is covering her hair.