How to change color in contourplot for just NAN values matplotlib-CodePudding

I am making a contourplot from a pandas dataframe (df in example), for which part of the graph are values that should should not be displayed. In the dataframe they are NaN values. The NaN values show up as a white area, but I would like to give this white area a color (for instance black). How can you achieve that? My code and the graph are as following:

plt.figure(1, figsize=(12, 12), dpi=600)
# plot contour lines
contours = plt.contour(df.columns,df.index, df, 8, colors = 'black')                                          
# add label to contour lines
contours.collections[0].set_label(parameter[choice]  ' [%]')                                
plt.clabel(contours, inline=True, fmt='%1.1f' , fontsize=fontsize1)                                           
# plot colormap
colormap = plt.contourf(df.columns,df.index, df, 800, cmap='RdYlGn', alpha=0.5)                                          # plot color map
# plot blue operational point
plt.plot(FU, V, 'bo', markersize=markersize, label='Nominal operation')     

# extra plot layout (not so important for example)
min_tick = df.to_numpy().min()
max_tick = df.to_numpy().max()
ticks = [np.linspace(min_tick, max_tick,3)]
cb = plt.colorbar(ticks = ticks)
cb.ax.tick_params(labelsize = fontsize1)
plt.xlabel('FU [-]', fontsize = fontsize2)
plt.ylabel('V [V]', fontsize = fontsize2)
plt.tick_params(axis='both', which='major', labelsize=fontsize1)
plt.grid(color = 'gray', linestyle=(0, (5, 10)), linewidth=1)
plt.legend(fontsize=fontsize2, loc = 'upper center')
plt.show
plt.savefig("contourplot "   parameter[choice]   " (V and FU)"  ".png")

In a

UPDATE: Thanks to help from Z Li, it works with the following code:

plt.contourf(df.columns,df.index, df, 800, colors = 'white')  
plt.gca().set_facecolor("black")  
colormap = plt.contourf(df.columns,df.index, df, 800, cmap='RdYlGn', alpha=0.5)

CodePudding user response：

Have you considered adding a white background to the plot first and then set background black?

plt.contourf(df.columns,df.index, df, 800, colors = 'white') 
colormap = plt.contourf(df.columns,df.index, df, 800, cmap='RdYlGn', alpha=0.5)

Original plot:

Without the white background, which is the issue you are facing:

With the white background: