Small refactorization + coverty fix

src/GraphMLWriter.hpp

@@ -208,6 +208,11 @@ struct vertex_node
 		create_prop<typename G::V_type>(attributes_names);
 	};
 
+	inline ~vertex_node()
+	{
+		delete [] attributes_names;
+	}
+
 #ifdef DEBUG
 	/*! \brief Constructor
 	 *

src/util.hpp

@@ -71,6 +71,8 @@ struct RGB getColor(int group, std::uniform_real_distribution<float> & d, std::d
 
 	float s = d(g);
 
+	group = group % 12;
+
 #ifdef ON_IO_UNIT_TESTS
 	s = 0.5;
 #endif