“ Here’s the thing about the stratosphere, the region between six and 31 miles up in the sky: If you really wanted to, you could turn it pink. Or green. Or what have you. If you sprayed some colorant up there, stratospheric winds would blow the material until it wrapped around the globe. After a year or two, it would fade, and the sky would go back to being blue. Neat little prank.”
This is my research area of specialty (I'm also strongly opposed to doing it), and I'd be shocked if it wasn't at least attempted in the next ten years.