Update examples to demonstrate different ways to show curvature

Author: mwaskom

examples/plot_label_foci.py

@@ -16,7 +16,7 @@
 """
 Bring up the visualization.
 """
-brain = Brain(subject_id, "lh", "inflated")
+brain = Brain(subject_id, "lh", "inflated", cortex=("gray", -2, 7, True))
 
 """
 First we'll identify a stereotaxic focus in the MNI coordinate system. This

examples/plot_probabilistic_label.py

@@ -16,7 +16,13 @@
 
 print(__doc__)
 
-brain = Brain("fsaverage", "lh", "inflated", cortex="low_contrast")
+brain = Brain("fsaverage", "lh", "inflated")
+
+"""
+Show the morphometry with a continuous grayscale colormap.
+"""
+brain.add_morphometry("curv", colormap="binary",
+                      min=-.8, max=.8, colorbar=False)
 
 """
 The easiest way to label any vertex that could be in the region is with