To open Display Options palette either select Display Options from Palettes pull-down menu or hit F9 key.
In Wire Frame display the darker lines are Iso Lines and show the curvature of the smooth surface. Iso Lines are automatically derived and are for visualization only. The lighter lines are the actual facets based on the current Display Resolution setting, see Tip #103. Drag the sliders to control the intensity of the lines. Uncheck the Facets option to view the Iso Lines only without the Facets.
In Shaded display the Iso Lines can be turned On or OFF. Facets are not visible in Shaded display.