its a tv problem. you probably have an ntsc tv which runs at 60hz i think. if you cant afford an hdtv, just get a pal tv and presto! gow3 demo in color. if you dont wana spend money on a new tv, i suggest you download games and demo using a us account. that way, the signals the game and ps3 sends to your tv will be compatible and it will be in color.
but when it comes to blu-ray disc based games, i havent encountered any problems. i've tried regions 1,2,3 and 4 blu-ray games on a pal ps3 using an ntsc tv and they all have color.