code: protected Object[] getExtendedCacheKeys(JComponent c) {
          Object[] extendedCacheKeys = null;
  
          if (state == Which.BACKGROUND_ENABLED) {
              extendedCacheKeys = new Object[] { getComponentColor(c, "background", defaultBackground, 0.0f, 0.0f, 0) };
          }
  
          return extendedCacheKeys;
      }
docs: {@inheritDoc}