My Chef tool has turned black

This is most likely due to a reaction to dishwasher detergent.
Please note that the older non-stick coated attachments are unsuitable for dishwashing.
It is possible to remove the black residue and restore the attachment to its original state.
As the attachment has been exposed to detergents containing alkaline you need to neutralise it by soaking it in lemon juice or vinegar for 24 hours.