You can choose to see the blocks with or without the thin black lines around each patch of the block using the Patch lines button in the Display toolbar.

find patch lines

 

Click to toggle this feature on and off.

patchlines

no patch line

Patch lines will be automatically turned ON if the Colorway selection is set to line drawings.

All the options available in the Display toolbar for the Blocks Panel can also be set in the Preferences dialog.