# credit to the Stack Overflow user in the source link
# choose one of these three possibilities

plt.plot(x, z3, '--', color='orange')           % String colorspec
plt.plot(x, z3, '--', color='#FFA500')          % Hex colorspec
plt.plot(x, z3, '--', color=[1.0, 0.5, 0.25])   % RGB colorspec