What “Englishman”?

After my Grandfather died in St. Kitts, W.I., I asked my mother, why my dark hair had bright red strains mixed in. She said it was because of that Engishman. What Engishman? You know the one who wrote that song they always play at funerals, “Amazing Grace”!!! My grandfather Samuel Newton was, (not sure how many greats) the grandson on John Newton, who was an English slaver, and later became a very well know man of God, and he wrote the famous hymn “Amazing Grace”. John Newton lived in St. Kitts and from of my research married an Englishwoman called Polly, they had no children. John Newton is well know in St. Kitts, there is even an area named after him called “Newton Ground”, an up to quite recently there was great discussion as to whether they should erect a statue to such and infamous character. This is a story that I have always wanted to know more about, the life of John Newton the “Englishman” in my family.