This command makes the color "black" invisible.
set object transparency objectid, flag
If you rather have a different color transparent other than black, you could set it the color key using this command.
set image colorkey Red, Green, Blue
Whenever you use the set image colorkey command, you must place it before the image you are loading. For instance If I wanted to load "Texture.bmp" and make the green color(0,100,0) transparent, the code would look like this.
set image colorkey 0,100,0
load image "texture.bmp", 1
make object sphere 10,100
texture object 10,1
set object transparency 10,0
