I think the Vidiot only process black and white video, in a similar way as the Cadet Video Input does, you can send colors, but they will be re-encoded at the RGB encoder stage along with the generated subcarrier, so does a bit of rainbow effect as both subcarrier are mixed together (and of course, original video color information will be lost as the signal will probably be blanked), that’s why it’s usually recommended to use a black and white video signal to start with. I guess that beside the sync generator, the Vidiot is mostly analog.
Lars commented recently to someone asking about decoder chips on Video Circuits, and he mentionned the TVP5150, so that’s probably what is used in the Chromagnon, which takes composite/YC/SD Component/HD Component (and maybe more? 
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