Conversation so far:
What is the definition?
Melungeons have been defined as having multiracial ancestry.
Were they considered a certain race on their own?
They did not exhibit characteristics that could be classified as those of a single racial phenotype.
Were there more dominant characteristics?
They did not exhibit characteristics that could be classified as those of a single racial phenotype.
Has the definition changed?
Melungeon are generally European American in appearance, often (though not always) with dark hair and eyes, and a swarthy or olive complexion.

Question: Has that definition be consistent?
Self-contained rewrite: Has the definition of Melungeon been consistent?