PC Engine Core Grafx 2 black and white picture problem

Hi,
Can anyone help?
I have a Japanese PC Engine Core Grafx 2 (im in the UK).

The sound is perfect and so is the picture, but is in black and white.
I have tried a few different games and a new AV cable, but it is still in black and white.

Thanks
paulie G

Is your TV 60Hz compatible? I remember on some older consoles when I was a kid, my TV didn't support 60Hz and the picture was black and white.

Or probably TV not NTSC compatible through composite.