removed shading when less than 3 forecasts

fixes issue SCECcode#214

csep/utils/plots.py

@@ -1758,9 +1758,9 @@ def plot_comparison_test(results_t, results_w=None, axes=None, plot_args=None):
                     markerfacecolor=facecolor, markeredgecolor=color,
                     markersize=markersize)
 
+    ax.set_xticks(numpy.arange(len(results_t)))
     ax.set_xticklabels([res.sim_name[0] for res in results_t],
                        rotation=xticklabels_rotation, fontsize=xlabel_fontsize)
-    ax.set_xticks(numpy.arange(len(results_t)))
     ax.set_xlabel(xlabel)
     ax.set_ylabel(ylabel, fontsize=ylabel_fontsize)
     ax.set_title(title)
@@ -1769,8 +1769,9 @@ def plot_comparison_test(results_t, results_w=None, axes=None, plot_args=None):
     ax.yaxis.set_major_locator(matplotlib.ticker.MaxNLocator(integer=True))
     ax.set_ylim([ylim[0], ylim[1]])
     ax.set_xlim([-0.5, len(results_t) - 0.5])
-    ax.bar(xTickPos, numpy.array([9999] * len(xTickPos)), bottom=-2000,
-           width=(xTickPos[1] - xTickPos[0]), color=['gray', 'w'], alpha=0.2)
+    if len(results_t) > 2:
+        ax.bar(xTickPos, numpy.array([9999] * len(xTickPos)), bottom=-2000,
+               width=(xTickPos[1] - xTickPos[0]), color=['gray', 'w'], alpha=0.2)
     fig.tight_layout()
 
     return ax