color "scribble-simple" eats up all memory & crashes

[Cevat Ustun <ustun Glue umd edu>]

I have written a simple application that draws a series of points 
given a starting point and gradually fills the screen (based on 
scribble-simple.c from the gtk tutorials). The black &white version
works flawlessly but the color version quickly swells up all the 
memory taken by X and ultimately crashes. Why? 

Below is the generalized version of draw_brush from the tutorial
(I tried both -1 and 16 for my pixmap depths):

void draw_brush( GtkWidget *drawing_area,
                         gdouble    x,
                         gdouble    y,
                         glong red,
                         glong green,
                         glong blue)
{
GdkColor color;
GdkGC *custom_gc;
GdkRectangle update_rect;

/*create new gc*/
custom_gc=gdk_gc_new(drawing_area->window);

/*define the color by its components*/
color.red=    red;
color.green=green;
color.blue=  blue;

/*allocate color*/
if(!gdk_colormap_alloc_color(gdk_colormap_get_system(), &color,
                                          FALSE,TRUE))
    g_error("couldn't allocate color");

gdk_gc_set_foreground(custom_gc, &color);


   update_rect.x = x ;
   update_rect.y = y ;
   update_rect.width = 1;
   update_rect.height = 1;

  gdk_draw_rectangle (pixmap,
                      custom_gc,
                      TRUE,
                      update_rect.x, update_rect.y,
                      update_rect.width, update_rect.height);

  gtk_widget_draw (drawing_area, &update_rect);
}