I've briefly read information on harrasment at work from south african law perspective. They suggest that a witness should corroborate the discriminating statements made by co-worker.
A brief story of what happened. I was walking down the hallway when the coworker in question says I should take his cup of coffee to the kitchen. I replied, "I'm not a domestic worker". He responded with, "Are you sure? You look like one".
What are my options, to pursue this matter further?