Quote: "
SET IMAGE COLORKEY
This command will set the general colorkey for all images. A colorkey allows you to specify a particular RGB colour that will be treated
as transparent by the image when used. Transparent pixels of an image are not drawn. You must use this command before loading or
grabbing an image in order that a suitable alpha map be generated from the transparent pixels of the desired image to be calculated.
The alpha map is then used to decide which pixels are drawn and which pixels are never rendered. Be aware that setting the color key
for the purpose of transparency will not work on images based on the PNG, TGA and DDS file format as these carry their own alpha
channel and describe their own pattern of transparency.
Syntax
SET IMAGE COLORKEY Red Value, Green Value, Blue Value
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Nuff said!
Best to use PNG or TGA file formats.