Well given that Blue flame is hotter than red flame and white flame is hotter than blue flame I would expect even higher efficiencies with the white cooler than the blue.
Drew, I have one of those, too. We call it the "Mash Coffin" because if you die while brewing it's big enough to be buried in! You'll be happy to know that the beer turns out almost as well as using a blue cooler. I guess you could paint it if you want that last .000001 %! Here's a pic of a couple of the Stoner Bros. stirring the mash for Old Stoner BW with a lacrosse stick. After we mashed in we realized we didn't have anything else big enough to stir with.