How many fullbrights there are depends on the colormap.lmp
By default it's the last two rows (the last 32 colours, of which the first 16 is the nice fire gradient and the second 16 is various useful fullbrights)
Colour 255 is transparent for sprites and 2d lmps and gfx.wad entries (excluding conchars, in which case it's black that's transparent)
I'm not on a computer with Quake installed atm so I can't be 100% sure but I think the shirt is the second row (16-31) and the pants are the goldy row (88-111).
Visit the quake wiki page for any more info ...