Strange rendering flicker

Question

I am rendering a pointcloud, but when I move the camera, points begin to flicker(youtu.be/wMTVID7NATo).

The strange thing is that the flicker disappear or is reduced when I change either the clear colour or the colour of the points. For example glClearColor(0, 0, 0, 1) and glColor3f(0.5f, 0.5f, 0.5f) causes flicker, but this flicker is gone when I use glClearColor(1, 1, 1, 1) or glColor3f(1, 1, 1).

What is causing this flicker and how can I get rid of it without changing clear or point colour?

Here is my code:

int main(int argc, char** argv) {
    glutInit(&argc, argv);   
    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE); 
    glutInitWindowSize(640, 480);
    mainWindow = glutCreateWindow("MyWindow");
    glutTimerFunc(1, timerRoutine, 0);
    glutDisplayFunc(displayFunc); 
    glutMotionFunc(motionFunc);
    glutMouseFunc(mouseFunc);

    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

    glEnable(GL_DEPTH_TEST); 
    glDepthFunc(GL_LEQUAL);
    glClearDepth(10.0f);  
}

void timerRoutine(int t) {
    glutPostRedisplay();
    glutTimerFunc(t, timerRoutine, 0);
}

void displayFunc() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glBegin(GL_POINTS);
    for (int i = 0; i < pointCount; ++i) {
        glColor3f(points[i].getIntensity(), points[i].getIntensity(), points[i].getIntensity());
        glVertex3f(points[i].getX(), points[i].getY(), points[i].getZ());
    }
    glEnd();
    glutSwapBuffers();
}

void mouseFunc(int x, int y, int z, int w) {
    if (x == 0) {
        if (y == 0) { //LMB Down 
            leftMouseButton = true;
        }
        else if (y == 1) { //LMB Up
            leftMouseButton = false;
        }
    }
}

void motionFunc(int x, int y) {
    if (leftMouseButton ) {
        camera.rotate(y, 0, x)); //Apply rotation to GL_MODELVIEW
    }
}