This is a big one. They make blue meth--the blue color is the signature trait, and all the other would-be meth makers, including Gale, "cannot account for the blue color."
In a couple episodes back, Skyler White had a sky blue wall in her office. She was also wearing a blue skirt when she fell into the blue pool which is reminiscent of the blue meth in its liquid stage--her life is being consumed by Walt's involvement in the meth manufacturing business. Remember this?
Remember the meth super lab was red, and that didn't end so well, and blood is red, so maybe we can assume blood means death? There was so much red in this half-season finale.
-The news anchor giving the news about the prison deaths was wearing red.
-Lydia's nails were red.
-Lydia's mug is red (and Walt almost killed her with the ricin) and Skyler's mug that the Crystal Blue persuasion montage connected them with was red.
Most striking to me was that the tarp the big pile of money was on, was red AND in a mirror image, the blanket that baby Holly gets laid on in the playpen was red.
Marie suddenly starts wearing yellow in this episode despite her life being ridiculously full of purple.
Here's a reminder of the insane amount of purple in Hank and Marie's house from Gliding All Over (Also notice the news anchor on the television reporting the prison deaths and her red outfit).
Then when they're all outside on Walt and Skyler's deck, she's wearing a yellow shirt and yellow bracelets. This is a huge change, considering Marie has worn purple almost every single time we've seen her. What does it mean? Does it signal a change in her role in the story now that Hank has just made a huge discovery? I can't wait to find out.
At one point during the amazing crystal blue persuasion montage, Lydia, Skyler and Walt are all wearing grey--perhaps to represent the new "Grey Matter" Empire?
Check it out around 1:20! (plus, the green barrels--money? And Lydia's red nails!)