diff --git a/svg.h b/svg.h
index 011c9f3..b34bb67 100644
--- a/svg.h
+++ b/svg.h
@@ -8,6 +8,6 @@
 void svg_begin(double width, double height);
 void svg_end();
 void svg_text(double left, double baseline, const std::string& text);
-void svg_rect(double x, double y, double width, double height, const std::string& stroke = "black", const std::string& fill = "black");
+void svg_rect(double x, double y, double width, double height, const std::string& stroke = "black", const std::string& fill = "red");
 void show_histogram_svg(const std::vector<size_t>& bins);
 #endif // SVG_H_INCLUDED