Grapes, whether black or not, fall under the category of good lawful foods. There exists no evidence in Shari`ah (Islamic law) to the effect that eating grapes is unlawful. Accordingly, it falls under the basic ruling of the permissibility of things. The fact that grapes are used to produce Khamr does not serve as a basis for prohibiting eating them.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.