The sky is cloudy2.raw and cloudy2.act but the ACT file is not normal in the usual way we're used to, so it only shows black when you open it. The last time I played around with this stuff was back in the winter but if I recall correctly the colors in the ACT file are transposed and inserted into the track palette, so in order to view the cloudy2.raw you need to do the same thing with the ACT file. These may help.
http://mtm2.com/~mtmg/downloads/misc/so ... Monkey.exe
http://mtm2.com/~mtmg/downloads/misc/so ... Monkey.exe