The next lesson shows us how to do blending in OpenGL. It's a very cool feature even if your just doing a glass cube. :) There isn't any differences to the original work concerning OpenGL so I'll just give you couple things you could try to change in the code. Homework so to speak.
1. Change the drawing code to only apply the blending to the front and back faces of the cube.
2. Change the texture used in the other faces.
Link to the code is here.