Fragment.glsl

varying lowp vec4 DestinationColor; // 1

void main(void) { // 2
    gl_FragColor = DestinationColor; // 3
}

gistfile1.m

- (void) render {
    glClearColor(0, 104.0/255.0, 55.0/255.0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT);



    // 1
    glViewport(0, 0, self.frame.size.width, self.frame.size.height);
//    2
    glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE,
            sizeof(Vertex), 0);
//    glVertexAttribPointer(_colorSlot, 4, GL_FLOAT, GL_FALSE,
//            sizeof(Vertex), (GLvoid*) (sizeof(float) * 3));


    float color[4] = {1,1,1,1};

    glUniform4fv(_colorSlot, 4, color);

    // 3
    glDrawElements(GL_TRIANGLES, sizeof(Indices)/sizeof(Indices[0]),GL_UNSIGNED_BYTE, 0);


    
    [_context presentRenderbuffer:GL_RENDERBUFFER];

}

Vertex.glsl

attribute vec4 Position; // 1
attribute vec4 SourceColor; // 2

varying vec4 DestinationColor; // 3

uniform mat4 Projection;

void main(void) { // 4
    DestinationColor = SourceColor; // 5
    gl_Position = Position; // 6
}