matplotlib transparency

# Basic syntax:
plt.plot(data, alpha=0.5)

# Note, the alpha parameter goes from 0 (fully transparent) to 1 
# 	(fully solid). It is especially useful when plotting overlapping
# 	histograms. 

plt.plot(x_values, y_values, "blue", linewidth=5, alpha=0.3)

plt.plot(x, y, 'r-', alpha=0.7)