i'm bumping this for phil
for winter sky i took the cmbb 1412, 1432, 1452 1024x256 opened with ms paint, made the size 1024x512 select all, move the sky to the bottom, use the dropper to pick a blue near the top, flood fill the white top section, save as...
nearly flat, with pines, bare trees, snow on the ground.
this works for bmps that are monochromatic at the top. in 800x600 you dont see the top unless you pan up. dont know if its good or bad in 1024 and up.
this takes a while for all the bmps. 3 day, dawn, dusk, overcast. but you dont need to do afrika.