I am looking for adjective describes the person whose origins cannot be identified based on his appearance features, accent, background ... etc. Some people has typical appearance features of middle Africans, Scandinavian, Chinese, Latin and so forth. I am aware that there is no strict line defines whether persons is coming from this area or that (e.g. a Scandinavian looking could be from USA). But generally speaking, if you met someone and you could not locate his/her origins due to overlapping and confusing features, what word can describe that person? I am looking for something more specific than (mixed).
In the U.S., where historically race was a more important social distinction than ethnicity or class (or, given the hypodescent standard, even skin color), people who are racially ambiguous are a subject of interest, both in popular (“10 most racially ambiguous celebrities!”) and intellectual (“What Are You?”: Racial Ambiguity and the Social Construction of Race in the US) sources.
By extension, ethnically ambiguous would be a broader application of the concept, and to my surprise, turns up almost the same number of Google.com results. A 2003 New York Times article suggests
ethnically neutral, diverse or ambiguous
I think few people would self-identify as "ambiguous" alone as a description of phenotype, or if they do it would be interpreted as androgynous. Rather, this is a label others apply. People who know they are of mixed descent could self-identify as multiracial (U.S. Census category), mixed race, or multiethnic— but in a modern professional setting in the U.S., calling attention to such characteristics is usually inappropriate and even outré.
For similar reasons, terms like mulatto or quadroon are considered outdated, and may be taken to be offensive.
There is this tailor shop at the edge of Manhattan where I met its owner of indiscernible racial origins. Was he from Bulgaria, Turkey, Turkmenistan, China or Afghanistan? I could hardly tell.
I came upon a lonely night, at a place far from the vicissitudes of human kindness and cruelty, when I encountered a being of indiscernible origin, and indiscernible horror-movie taxonomy, whose constant vicissitude in behaviour made it impossible to tell if he was vampire, werewolf, frankensteinian, angel, devil or polydemiglot (being conversant in various angelic/demonic tongues).
According to our holy book of sacred witchery, one of the seven spiritual gifts is discernment. In fact, we hold that discernment is the most supreme of all gifts. For it gives the giftee the ability to discern the various species of spirits and their hidden intents, and thus allowing the holder of the gift, the giftee, the ability to sway and exploit the indiscernible confusion the spirits cast upon each other.
Difficult or impossible to discern or perceive; imperceptible: an indiscernible increase in temperature.
The American Heritage® Dictionary of the English Language, Fourth Edition copyright ©2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
untypical: not representative of a particular type, person, etc.
nontypical: not having the distinctive qualities of a particular type of person or thing; uncharacteristic
type: qualities common to a number of individuals that distinguish them as an identifiable class, as the morphological, physiological, or ecological characters by which relationship between organisms may be recognized.
That being said, what I would typically say of that person is that they are of unidentifiable origin.
Lacking distinguishing characteristics or features
"her face was as round and red as a harvest-moon and almost as featureless." – Anne of The Island by Lucy Maud Montgomery.