blue snow??

It's moments like this that make me fear for the future of our planet. I came across this sight at a head office for another company, where they had obviously used some kind of chemical/salt to melt ice and snow on the sidewalks. But why blue? Does it have to be blue? could you not just use natural salts? (which in itself can be pretty harmful) Why colour it blue and add that extra bit of harmfulness to it?? I mean, I love the colour blue and all... but that's clearly a bad thing in this case