Just a quick observation - if you see color through Composite but not with SVideo, and you are using SCART, it might be an issue of input format switching.
The SCART standard contains three input formats: Composite, SVideo and RGB.
Some of the formats share the same pins in the connector (for example, pin 15 is used as Red input in RGB mode and Chroma input in SVideo mode).
Pin 16 is used to select between Composite & RGB, but there is no way to select SVideo.
That is up to the TV to either auto-detect, or to let you manually switch.
I suggest you check your TV manual to see if you can manually set it to use SVideo.