The best you can AFAIK is to give “black” as parameter and use reflection:
// Put this at the top of your script
using System.Reflection;
public void ColorMatC( string c )
{
Type type = typeof(Color);
var property = type.GetProperty(c, BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static);
if( property == null )
throw new System.ArgumentException("No property named " + c + " exist in the Color type");
Color color = (Color) property.GetValue(null);
Debug.Log( color ) ;
}