-floodfill does not seem to honor the fuzz settings!
(am I doing something in error?)
convert -size 100x100 xc:white \
-fill none -stroke red -strokewidth 2 \
-draw "circle 50,50 75,50" \
tmp_circle_open.png
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convert -size 100x100 xc:white \
-fill none -stroke red -strokewidth 2 \
-draw "circle 50,50 75,50" \
-fill red -floodfill +50+50 white \
tmp_circle_floodfill0.png
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convert -size 100x100 xc:white \
-fill none -stroke red -strokewidth 2 \
-draw "circle 50,50 75,50" \
-fill red -fuzz 100% -floodfill +50+50 white \
tmp_circle_floodfill100.png

Note I also get the same results using:
-fill red -fuzz 100% -draw "color 50,50 floodfill" \
rather than
-fill red -fuzz 100% -floodfill +50+50 white \
But I am not sure if -draw should honor the fuzz setting? Should it?