I don't know why Falko chosen #ffa0ff (255,160,255) as "transparent", it's always been #ff00ff (255,0,255) - pure purple color (warboy given that palette long long time ago).
I couldn't find these act files, thus created my own, all palettes of xcom1/xcom2. Including background palettes (actual colors are in the range of ingame background colors - 224..239).
All "special" battlescape colors like colorgroup15 for xcom1 and color255 for tftd are properly replaced, transparent color0 = #ff00ff(255,0,255)