code: private void setGridAxisColors(ro.nextreports.jofc2.model.Chart flashChart, XAxis xAxis, YAxis yAxis) {
          boolean isHorizontal = chart.getType().isHorizontal();
          Color xGridColor = chart.getXGridColor();
          Color yGridColor = chart.getYGridColor();
          if (xGridColor != null) {
              getXAxis(xAxis, yAxis, isHorizontal).setGridColour(getHexColor(xGridColor));
          }
          if ((chart.getXShowGrid() != null) && !chart.getXShowGrid()) {
              if (flashChart.getBackgroundColour() == null) {
                  getXAxis(xAxis, yAxis, isHorizontal).setGridColour(getHexColor(DEFAULT_BACKGROUND));
              } else {
                  getXAxis(xAxis, yAxis, isHorizontal).setGridColour(flashChart.getBackgroundColour());
              }
          }
          if (yGridColor != null) {
              getYAxis(xAxis, yAxis, isHorizontal).setGridColour(getHexColor(yGridColor));
          }
          if ((chart.getYShowGrid() != null) && !chart.getYShowGrid()) {
              if (flashChart.getBackgroundColour() == null) {
                  getYAxis(xAxis, yAxis, isHorizontal).setGridColour(getHexColor(DEFAULT_BACKGROUND));
              } else {
                  getYAxis(xAxis, yAxis, isHorizontal).setGridColour(flashChart.getBackgroundColour());
              }
          }
      }
docs: to hide a grid we set its color to chart background color