are you using a scart lead or a plain old RF aerial lead?
when i first played an NTSC game on a PAL PSX on a PAL TV it was in black and white. i binned my RF cable and bought a scart - then it was in colour. only cost a fiver and improved the picture no end.
of course it might be different with having an NTSC PSX, so you could buy a converter (as already suggested), or use an NTSC-compatible TV (if thats an option, most newer PAL TVs are NTSC compatible)
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Chrysler D platform picture