White Rectangle on a Blue Background

First, the Basic Idea

In the init callback: In the display callback:

Here's the OpenGL code for init and display:

For init:
     glClearColor (0.0f, 0.0f, 1.0f, 0.0f);
     glColor3f (1.0f, 1.0f, 1.0f);
     glMatrixMode (GL_PROJECTION);
     glLoadIdentity ();
     gluOrtho2D (0.0f, 1.0f, 0.0f, 1.0f);
For display:
     glClear (GL_COLOR_BUFFER_BIT);
     glBegin (GL_POLYGON);
          glVertex3f (0.25, 0.25, 0.0);
          glVertex3f (0.75, 0.25, 0.0);
          glVertex3f (0.75, 0.75, 0.0);
          glVertex3f (0.25, 0.75, 0.0);
     glEnd ();
     glFlush ();