This is from the Boston Evening Post September 22 1756:
“Thursday last in the afternoon Mark, a negro man and Phllis a negro woman, both servants of Captain John Codman of Charlestown, were executed at Cambridge for poisoning their said master. The man was hanged and the woman burnt at the stake about 10 yards distant from the gallows. They both died Penitent. ”
For all the differences in law between the races, this couple seem to have been treated exactly the same as if they had been white.
The woman was treated like a witch while the man as a common criminal.
The last comment suggests they were practicing Christians.