tetraflexagon_diagram: do not use a fill_color for the template tiles

Pass fill_color=None when drawing the template to make it only
a wireframe reference, as it is done for the hexaflexagon case.

This also makes the result more usable as the user is able to view the
content layers more clearly without filled squares on top.

diff --git a/src/flexagon/tetraflexagon_diagram.py b/src/flexagon/tetraflexagon_diagram.py
index d64ce32..5d810de 100755 (executable)
--- a/src/flexagon/tetraflexagon_diagram.py
+++ b/src/flexagon/tetraflexagon_diagram.py
@@ -94,7 +94,9 @@ class TetraflexagonDiagram(object):
         side = self.tile_side
         color = self.squares_color_map[tile.square.index]
 
-        self.backend.draw_rect_from_center(cx, cy, side, side, theta, color)
+        self.backend.draw_rect_from_center(cx, cy, side, side, theta,
+                                           stroke_color=color,
+                                           fill_color=None)
 
         corners_labels = "ABC"
         corner_text = corners_labels[tile.square.index] + str(tile.index + 1)