Color film is based on silver halides but has built-in dye couplers and filters to represent the color details. Any color film developed with chemicals intended for black and white film will come out as black and white film. There is a Flickr group dedicated to the practice: https://www.flickr.com/groups/c41inbw/pool/

Colour film gives the same results as black and white film when developed with the black and white process, except for the orange base.

IMO it's not really an interesting thing to do unless you don't have a choice.