I asked HiTech about clutter overlays for user created terrains.  (ground effects toggled by Ctrl C)
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You need to make 4 files they are watdet.bmp, watdet.bma, landdet.bmp, and landdet.bma. 
The bmps are 256 color, the bma's are 256 grayscale for the alpha channel. 
The bma extension is a 256 bit grayscale bmp renamed to bma.
Place these into your terrain directory and it should work. 
HiTech
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Thanks for the info HT.