Difficulty rendering an octahedron (2 pyramids attached at the bottom to each other)

[Kev Lee]

I am having difficulty with my homework project rendering an octahedron by modifying an existing project that renders a pyramid. The hint given is to change the vertices, colors, and indices objects. I did that but the best I could generate is the existing pyramid with 1 or 2 faces of the inverted pyramid shown while it is rotating on screen. I have been changing the order of the indices and vertices but still can not solve the problem. I think these values are correct if I draw it on paper. I would appreciate some tips to solve the problem as I have not make any progress after days of fruitless tinkering. Perhaps I need to modify other code? Thanks in advance! Here are the values of the vertices, colors, and indices:

private float[] vertices = { // 6 vertices of the pyramid in (x,y,z)
-1.0f, -1.0f, -1.0f, // 0. left-bottom-back
1.0f, -1.0f, -1.0f, // 1. right-bottom-back
1.0f, -1.0f, 1.0f, // 2. right-bottom-front
-1.0f, -1.0f, 1.0f, // 3. left-bottom-front
0.0f, 1.0f, 0.0f, // 4. top

//added vertex
0.0f, -3.0f, 0.0f // 4. bottom
};

private float[] colors = { // Colors of the 6 vertices in RGBA
0.0f, 0.0f, 1.0f, 1.0f, // 0. blue
0.0f, 1.0f, 0.0f, 1.0f, // 1. green
0.0f, 0.0f, 1.0f, 1.0f, // 2. blue
0.0f, 1.0f, 0.0f, 1.0f, // 3. green
1.0f, 0.0f, 0.0f, 1.0f, // 4. red

//added color
1.0f, 1.0f, 0.0f, 0.0f // 5. yellow
};

private byte[] indices = {
2, 4, 3, // front face (CCW) - same as 4,3,2 or 3,2,4
4, 2, 1, // right face - same as 2,1,4 or 1,4,2
0, 4, 1, // back face - same 4,1,0 or 1,0,4
4, 0, 3, // left face - same 0,3,4 or 3,4,2

// inverted pyramid
3, 5, 2,
2, 5, 1,
1, 5, 0,
3, 5, 0,
};