There's an alternative method of connecting your initial textures if you're using the tutorial mentioned above. Instead of connecting each texture's Out Color attribute to the condition utility's Color 1 and color 2 attributes, try this instead:

Connect the outer texture to the condition node's "colorIfTrue" attribute. Then do the same for the texture you want on the inside, except connect it to the condition node's "colorIfFalse" attribute. So in a few short steps, here's the whole thing:

1. Create a blinn, a condition node, and two textures (in my example below, a wood texture and checkerboard).

2. Middle-mouse drag and drop the condition utility node onto the blinn and choose "color".

3. Now, connect the textures (mmb, click and drag) as I mentioned above. If we want the wood on the outside of our object (the direction the normals are facing), you'll connect that to the condition utility's "colorIfTrue" attribute. The blinn will take on the color of whichever you have plugged into "coloriftrue." So, connect the other texture to the condition node's "colorIfFalse".

4. Create a sampler info node and middle-mouse drag and drop it on the condition node and choose "other" which will open the connection editor. Connect Sampler Info's "Flipped Normal" into the condition's "First Term" and you should be good to go.