CANT PLAY GENUINE US GRAN TURISMO IN COLOUR??

[skanky]

Please help.I am using a game hunter plug in cart on my 7502 playstation,and I have 2 original NTSC games,gran turismo and tekken2.My tv is NTSC/PAL compatible but will only display these genuine games in black and white.I am using the standard psx tv rf lead,.Do I need a scart cable???All other back ups of uk/us/jap games work with colour no problem.Helllllllllllp!!!!!!!!
And I have also switched between PAL and NTSC on the game hunter cart which made no difference.