S-Video signals are generally connected using 4-pin mini-DIN connectors using a 75 ohm termination impedance. Today, S-Video can be transferred through SCART connections as well. S-Video and RGB are mutually exclusive through SCART, due to the S-Video implementation using the pins allocated for RGB. Most SCART-equipped televisions or VCRs (and almost all of the older ones) do not actually support S-Video, resulting in a black-and-white picture if attempted to use, as only the luminance signal portion is used. Black-and-white picture in itself can also be a sign of incompatible colour encoding, for example NTSC material viewed through a PAL-only device.
I have bought a new scart-composite cable and now everything is working fine.
The above information is provided by Mr. Jeroen Mooijekind, thank him!