Megadrive 60Hz black and white

[sandokan]

Hello, first thanks to all who is getting this forum so great. I'm spanish man and is the first time I post here.

Yesterday I made an RGB cable getting the instructions on a spanish web and it works very well on 50Hz mode, but when I switch it to 60Hz mode, the screen appears in black and white mode. Don't know why because it supossed its an RGB cable and my TV supports 60Hz (tested with other new generation systems).

Can anyone help me please?

Thanks again and sorry for my poor english