Deleting Material Appearance

I have created custom materials and added appearances. However, now I want to delete these appearances and revert back to the default gray color. The issue is that when I go into the Material Properties and Edit the appearance I delete the color and save the material, but when I go back into the material library, the color is still attached to the material. If I have multiple appearances in the material file, all but the defaulted appearance gets deleted just fine..it is only the defaulted appearances that stay.  Any suggestions?

Thanks