I think that's some addon.
Must not be payware (like REX, which is really good though), but maybe you can find some generic replacement when looking at freeware libraries.

The REX thing gives you tons of such textures to chose from, among clouds, water, lights and all sorts of things. They also give you snow in the winter times and an altered wet effect.
Don't worry, this doesn't harm addon airports, only the default ones as their textures get replaced. And also the replacement of the default textures shouldn't harm fps at all unless you chose the HD ones, but even those run fine on a fairly modern system.

Commonly used products are FEX (Flight Environment X) or the mentioned REX (Real Environment X). Just google them, pictures will come up.

I have REX and it's great! That's how I've managed to get sunrise/sunset looking great in some of my recent posts.