This has probably been posted before but it is worth repeating.

If you search the mortality index at ancestry.com for the county you are researching you will find Free Blacks indicated as "FB".

For example in Loudoun county VA:

Surname: FENTON -FB- CUBBINS
Year: 1850
County: LOUDOUN CO.
State: VA
Age: 03
Gender: M
Month of Death: JUL
State of Birth: VA
ID#: MRT46_1607
Occupation: NONE LISTED
Cause of Death: LUNGSINFLAM

Surname: ROSE -FB- FIELDS
Year: 1850
County: LOUDOUN CO.
State: VA
Age: 06
Gender: F
Month of Death: AUG
State of Birth: VA
ID#: MRT46_2229
Occupation: NONE LISTED
Cause of Death: UNKNOWN

In 1860 PA - people have Negro or Malato as a middle name in the index:

Surname: MARY JANE NEGRO BROWN
Year: 1860
County: CHESTER CO.
State: PA
Age: 3M
Gender: F
Month of Death: JAN
State of Birth: PA
ID#: MRT317_9659
Occupation: NONE LISTED
Cause of Death: UNKNOWN

Surname: ELIZABETH MALATO GREEN
Year: 1860
County: CHESTER CO.
State: PA
Age: 14
Gender: F
Month of Death: APR
State of Birth: PA
ID#: MRT317_9685
Occupation: NONE LISTED
Cause of Death: CONSUMPTION

In 1860 NC - they use black:

Surname: JAMES -BLACK- PEOPLES
Year: 1860
County: MECKLENBURG CO.
State: NC
Age: 1
Gender: M
Month of Death: AUG
State of Birth: NC
ID#: MRT293_4486
Occupation: NONE LISTED
Cause of Death: TYPHOID FEV