So I am Indian with what you could consider light brown skin. If I were alive during the middle ages and lived in say England what ethnicity would the consider me? Would they just assume I'm a very light black person? Or perhaps would they just think I was a tan white person? How would this affect my social standing?
Post-Roman England? Anglo-Saxon England? Viking England? Norman England? England of the Magna Carta? Late Medieval Elizabethan England?
The middle ages stretched almost a thousand years with a lot of different societal, cultural and religious differences in that time.
Regardless, we have no evidence that ethnicity separated from religion mattered; for most of this period being Christian mattered, being Jew or Moor/Moslem mattered. Someone would wonder if you were a free man or not, and depending on the community and time period, they would even wonder how orthodox your Christian beliefs were. There are almost no medieval records where see an assumption of religion based on skin colour. We might see some race definitions in the very late medieval/beginnings of the early modern period.