I've attached a demo version with replaced clouds. Make sure you have the default color scheme set in the options or you'll just see normal clouds.
The pain with replacing sprites is you don't have the same freedom as when making terrains. You're limited to a fixed 90 color palette and that palette is different depending on if you use the default color scheme (which uses the gfx0.dir sprites file) or the alternate color scheme for anomalous vision (which uses the gfx1.dir sprites file). Sadly, the game doesn't allow you to borrow colors from the terrain assets. So you have to make your replacement sprites work with those 2 palette sets (by making 2 versions of your sprite) and they are quite different. For example, converting this new sprite to the gfx1 palette looked awful, whereas I just about got away with it in the gfx0 palette (with a lot of diffusion dithering!).
Anyways - it won't be replacing the original but it's a fun little demo. When full color is eventually implemented it will open up some very cool possibilities for the game, especially if Deadcode implements the wkTerrainSync feature set; being able to replace water and sprites, having multiple background layers. It would also be cool to support multiple different debris sprites at the same time and be able to set the amount/density on screen for each.