glPushMatrix();
glRotatef(theta, 0.0f, 0.0f, 1.0f);
glBegin(GL_QUADS);
glColor3f(1.0f, 0.0f, 0.0f); glVertex2f(-0.8f, -0.8f);
glColor3f(0.0f, 1.0f, 0.0f); glVertex2f(-0.8f, 0.8f);
glColor3f(0.0f, 0.0f, 1.0f); glVertex2f(0.8f, 0.8f);
glColor3f(0.0f, 0.0f, 1.0f); glVertex2f(0.8f, -0.8f);
glEnd();
glPopMatrix();
where theta is whatever the angle you want to rotate it by is (in Radians, obviously). So long as theta is constant, it will not be rotated any more. It should only 'spin' if you change constantly increment theta.