I'm not sure I understand what you are asking.
If I was trying to detect a black object I would go with either a 'through beam' type sensor - where a transmitter sends a light beam to a receiver and the black object blocks the beam as it goes by. Or a 'retroreflective' sensor where the light beam goes from the photo-eye to a reflector and back. (Again, the black object would block the beam and be detected.)
In another application where we work we have white paper, and we want to detect a black mark on the paper. In this case a 'proximity' photo-eye does the job. Adjust the sensitivity of the eye such that it reliably picks up the white paper (or brown or blue) but does not pick the reflection from the black mark. (In this case a flat black tape stuck to the white paper.)
Banner has a nice series of photo eyes for these purposes.
Poet.