Enabling light0 in GLKit results in loss of color

Question

I've been modifying some sample code from OpenGL ES 2 tutorials. I can set the GLKBaseEffect to use a constant colour. Now, when I go to add light to the scene, the colour is lost and I am left with 2 black cubes.

Below is the draw method:

 - (void)draw
{
    GLKMatrix4 xRotationMatrix = GLKMatrix4MakeXRotation(rotation.x);
    GLKMatrix4 yRotationMatrix = GLKMatrix4MakeYRotation(rotation.y);
    GLKMatrix4 zRotationMatrix = GLKMatrix4MakeZRotation(rotation.z);
    GLKMatrix4 scaleMatrix = GLKMatrix4MakeScale(scale.x, scale.y, scale.z);
    GLKMatrix4 translateMatrix = GLKMatrix4MakeTranslation(position.x, position.y,     position.z);

    GLKMatrix4 modelMatrix =
    GLKMatrix4Multiply(translateMatrix,
    GLKMatrix4Multiply(scaleMatrix,
    GLKMatrix4Multiply(zRotationMatrix,
    GLKMatrix4Multiply(yRotationMatrix, xRotationMatrix))));

    GLKMatrix4 viewMatrix = GLKMatrix4MakeLookAt(0, 0, 3, 0, 0, 0, 0, 1, 0);
    effect.transform.modelviewMatrix = GLKMatrix4Multiply(viewMatrix, modelMatrix);
    effect.transform.projectionMatrix = GLKMatrix4MakePerspective(0.125*M_TAU, 2.0/3.0, 2, -1);

    effect.useConstantColor = YES;
    effect.constantColor = redColor;
    [effect prepareToDraw];

    glEnable(GL_DEPTH_TEST);
    glEnable(GL_CULL_FACE);

    glEnableVertexAttribArray(GLKVertexAttribPosition);
    glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 0, triangleVertices);

// Sticking with constant color as opposed to per-vertex vertex shading for now...
//    glEnableVertexAttribArray(GLKVertexAttribColor);
//    glVertexAttribPointer(GLKVertexAttribColor, 4, GL_FLOAT, GL_FALSE, 0, triangleColors);

    glDrawArrays(GL_TRIANGLES, 0, 36);

    glDisableVertexAttribArray(GLKVertexAttribPosition);
    glDisableVertexAttribArray(GLKVertexAttribColor);
}

I enable the light in my initialise static method :

+ (void)initialize {
    if (!initialised) {
        vertices[0] = GLKVector3Make(-0.5, -0.5,  0.5); // Left  bottom front
        vertices[1] = GLKVector3Make( 0.5, -0.5,  0.5); // Right bottom front
        vertices[2] = GLKVector3Make( 0.5,  0.5,  0.5); // Right top    front
        vertices[3] = GLKVector3Make(-0.5,  0.5,  0.5); // Left  top    front
        vertices[4] = GLKVector3Make(-0.5, -0.5, -0.5); // Left  bottom back
        vertices[5] = GLKVector3Make( 0.5, -0.5, -0.5); // Right bottom back
        vertices[6] = GLKVector3Make( 0.5,  0.5, -0.5); // Right top    back
        vertices[7] = GLKVector3Make(-0.5,  0.5, -0.5); // Left  top    back

        colors[0] = GLKVector4Make(1.0, 0.0, 0.0, 1.0); // Red
        colors[1] = GLKVector4Make(0.0, 1.0, 0.0, 1.0); // Green
        colors[2] = GLKVector4Make(0.0, 0.0, 1.0, 1.0); // Blue
        colors[3] = GLKVector4Make(0.0, 0.0, 0.0, 1.0); // Black
        colors[4] = GLKVector4Make(0.0, 0.0, 1.0, 1.0); // Blue
        colors[5] = GLKVector4Make(0.0, 0.0, 0.0, 1.0); // Black
        colors[6] = GLKVector4Make(1.0, 0.0, 0.0, 1.0); // Red
        colors[7] = GLKVector4Make(0.0, 1.0, 0.0, 1.0); // Green

        int vertexIndices[36] = {
            // Front
            0, 1, 2,
            0, 2, 3,
            // Right
            1, 5, 6,
            1, 6, 2,
            // Back
            5, 4, 7,
            5, 7, 6,
            // Left
            4, 0, 3,
            4, 3, 7,
            // Top
            3, 2, 6,
            3, 6, 7,
            // Bottom
            4, 5, 1,
            4, 1, 0,
        };

        for (int i = 0; i < 36; i++) {
            triangleVertices[i] = vertices[vertexIndices[i]];
            triangleColors[i] = colors[vertexIndices[i]];
        }

        effect = [[GLKBaseEffect alloc] init];
        effect.lightingType = GLKLightingTypePerVertex;
        effect.lightModelAmbientColor = GLKVector4Make(0.3f, 0.3f, 0.33f, 1.0f);
        effect.light0.enabled = GL_TRUE;
        effect.light0.diffuseColor = GLKVector4Make(1.0f, 0.4f, 0.4f, 1.0f);

        initialised = YES;
    }
}

The following are screenshots of when the lighting is disabled (red color) and disabled (black colour)

Answer 1

Lighting requires your vertices to have both position and normal attributes -- you appear to only have position.

Answer 2

You may also need to enable the color material property:

self.effect = [[GLKBaseEffect alloc] init];
self.effect.colorMaterialEnabled = GL_TRUE;