CASE 1: no opacity set on any layers

CASE 2: opacity set to .99 on overlays but not on basemap

CASE 3: opacity set on overlays but not on basemap, zIndex option set to 0 on basemap

CASE 4: opacity set to .99 on overlays but set to 1 on basemap

CASE 5: opacity set to .99 on all layers

CASE 6: opacity set to .99 on 1st and 3rd layers and 1 on middle layer