Bioluminescent clouds

Some clouds, it turns out, contain large populations of bacteria. There is some complex ecology going on up there, because the bacteria act as nucleation sites for water droplets, and can also influence the freezing of those droplets. Thus, these bacteria have impacts on rainfall and snowfall. It's very likely, in fact, that the bacteria impact clouds in a way that is beneficial to the bacteria.

Now, this is all very interesting and eco and gaia and all that, but who (frankly) gives a flying fuck? Well, technically the bacteria don't - although some of them do have the equivalent of sexual reproduction.

Howevertheless, the presence of cloudborne bacteria open up unlimitless possibilities. In particular, some bacteria are bioluminescent, and others can generally be engineered to be so. Note that I'm not talking about fluorescence (a la GFP) here, but actual bioluminescence. With a bit of tinkering we can get most colours from red through to greeny-blue.

So.

The first step in the process is to grow up shedloads of these bacteria, in a chosen colour, in a regular lab fermenter. We're talking a few hundred litres of dense culture, amounting to maybe 10^15 bacteria.

The second step is to fly through some nice low clouds as evening approaches, spraying these bacteria as a fine mist.

The third step is the clever one: there is no third step. We just sit back and enjoy the ghostly green glow of a cloud, perhaps swirling and mixing with the red glow of another cloud, and finally dissipating as the bacteria get out-competed by their sleeker, better- adapted non-luminous cousins.