diff --git a/normdist.py b/normdist.py
index 6483e1f..ea3456d 100644
--- a/normdist.py
+++ b/normdist.py
@@ -6,11 +6,19 @@ from scipy.stats import norm
 
 mean = 1
 stddev = 5
+lowerbound = -1
+upperbound = 1
 x = np.linspace(-10, 10
                 , 1000)
-plt.plot(x, norm.pdf(x, mean, stddev), 'b-', label='Normal Distribution')
+y = norm.pdf(x, mean, stddev)
+plt.plot(x, y, 'b-', label='Normal Distribution')
+coloredregion = (x >= lowerbound) & ( x <= upperbound ) #select x values
+plt.vlines([lowerbound, upperbound], 0, plt.ylim()[1])#ylim returns [bot, top]
+
+plt.fill_between(x, 0, y, where=coloredregion, color="grey", alpha=0.5, label="Design Range")
 plt.xlabel('X')
 plt.ylabel('Probability Density')
 plt.legend()
 plt.grid(True)
 plt.show()
+