Does conditioner strip hair colour?

My mother in law told me that her hairdresser told her that using conditioner strips hair colour. Now this doesn't mnake sense to me as I know that the molecules in shampoo are what attach themselves to dirt in your hair and then when you rinse the shampoo takes the dirt with it. And conditioner smoothes the cuticles of the hair so if it is true that it strips hair colour, then how?