I had a few questions about how this was done in basic:
Instead of trying to walk through it, I'm just going to point to a tutorial on here that might clear things up.
The trick in this specific photo was to try and have the only blue in the entire shot be in the sky. I wish I'd had more time to get better light/angles, but c'est la vie. The truly observant will note that some blue was left in the frames of the glasses used to sticky-tape the mirrors on.
