Is there a mask image colour command in GLB?
If you mean to set the color for transparency it is:
SETTRANSPARENCY RGB(255,0,128)
If you set the background color to RGB(255,0,128) that will be transparent when you draw sprites.
SETTRANSPARENCY should do it - give it the rgb value of the colour you want to use as a mask.
Alternatively, use PNG's with a mask.
Ah - Moru got there first =D
Thanks guy's, that did just the job :)