Two of my ps2 games display as gray/no colour when I try to play them?

I remember having similar problems with my games but they were always because of PAL and NTSC. sooo im going to have a guess and say it might be caused by the disc. scratches or where the game is made? those are possible but a little doubtful. sorry thats all the help i can give since i have no more information and im not there :\