code: public static Expression desaturate(Generator generator, FunctionCall input) {
          Color color = input.getExpectedColorParam(0);
          int decrease = input.getExpectedIntParam(1);
          return changeSaturation(color, -decrease);
      }
docs: Decreases the saturation of the given color by N percent.
  
  @param generator the surrounding generator
  @param input     the function call to evaluate
  @return the result of the evaluation