How do I make an open cube (missing one surface) without getting effect where sides are mirrored or switched in OpenGL?

I am trying to create a cube that has one surface missing (an open box in effect), but when I make it, the side opposite to the missing side gets super imposed on where the opening should be when the object is rotated.

Here is what I mean: View of Front and back of Cube angled:

How do I get rid of the weird color overrides going on?

Here is my current code:

#include <stdio.h>
#include <stdarg.h>
#include <math.h>
#include <stdlib.h>
#include <GL/glut.h>


void display();
void viewButtons();


double rotationY = 0;
double rotationX = 0;

void display()
{
 //Clear the screen and clear z-buffer
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Reset transformations
    glLoadIdentity();

// Rotate when user changes rotate_x and rotate_y
    glRotatef(rotationX, 1.0, 0.0, 0.0);
    glRotatef(rotationY, 0.0, 1.0, 0.0);
    glBegin(GL_POLYGON);
//Vertices and colors
    glColor3f(1.0, 0.0, 0.0);     
glVertex3f(0.5, -0.5, -0.5);      // P1 is red
glColor3f(0.0, 1.0, 0.0);    
glVertex3f(0.5, 0.5, -0.5);      // P2 is green
glColor3f(0.0, 0.0, 1.0);     
glVertex3f(-0.5, 0.5, -0.5);      // P3 is blue
glColor3f(1.0, 0.0, 1.0);     
glVertex3f(-0.5, -0.5, -0.5);      // P4 is purple

glEnd();

/*// White side - BACK
glBegin(GL_POLYGON);
glColor3f(1.0, 1.0, 1.0);
glVertex3f(0.5, -0.5, 0.5);
glVertex3f(0.5, 0.5, 0.5);
glVertex3f(-0.5, 0.5, 0.5);
glVertex3f(-0.5, -0.5, 0.5);
glEnd();*/

// Purple side - RIGHT
glBegin(GL_POLYGON);
glColor3f(1.0, 0.0, 1.0);
glVertex3f(0.5, -0.5, -0.5);
glVertex3f(0.5, 0.5, -0.5);
glVertex3f(0.5, 0.5, 0.5);
glVertex3f(0.5, -0.5, 0.5);
glEnd();

// Green side - LEFT
glBegin(GL_POLYGON);
glColor3f(0.0, 1.0, 0.0);
glVertex3f(-0.5, -0.5, 0.5);
glVertex3f(-0.5, 0.5, 0.5);
glVertex3f(-0.5, 0.5, -0.5);
glVertex3f(-0.5, -0.5, -0.5);
glEnd();

// Blue side - TOP
glBegin(GL_POLYGON);
glColor3f(0.0, 0.0, 1.0);
glVertex3f(0.5, 0.5, 0.5);
glVertex3f(0.5, 0.5, -0.5);
glVertex3f(-0.5, 0.5, -0.5);
glVertex3f(-0.5, 0.5, 0.5);
glEnd();

// Red side - BOTTOM
glBegin(GL_POLYGON);
glColor3f(1.0, 0.0, 0.0);
glVertex3f(0.5, -0.5, -0.5);
glVertex3f(0.5, -0.5, 0.5);
glVertex3f(-0.5, -0.5, 0.5);
glVertex3f(-0.5, -0.5, -0.5);
glEnd();

glFlush();
glutSwapBuffers();


}

void viewButtons(int button, int x, int y)
{
if (button == GLUT_KEY_RIGHT)
    rotationY += 5;

else if (button == GLUT_KEY_LEFT)
    rotationY -= 5;

else if (button == GLUT_KEY_UP)
    rotationX += 5;

else if (button == GLUT_KEY_DOWN)
    rotationX -= 5;

//update display
glutPostRedisplay();
}
int main(int argc, char **argv) {

// init GLUT and create window
// init GLUT and create Window
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowPosition(100, 100);
glutInitWindowSize(720, 640);
glutCreateWindow("Room with objects");

// register callbacks
glutDisplayFunc(display);
glutSpecialFunc(viewButtons);
// enter GLUT event processing cycle
glutMainLoop();

return 1;
}