His dad was a Spaniard of some rank, and his mom, a Negress and former slave. Martin was illegitimate and his father soon abandoned the boy along with his mom and his sister.
When Martin was canonized I recall them making a big deal of the fact that he was of mixed race. I remember thinking that his race made no difference to me - I simply admired him as a humble lay-brother saint I hoped to imitate one day.
Read more on St. Martin here.