It is a little known fact that Rotobot was trained in the colour space of the Internet sRGB or a Gamma of 1.8-2.2 with respect to light. This means that if your footage is not in sRGB it is not going to detect as well as if it were in sRGB. So how do you do that?
Using a OCIO Colorspace Transform node, you can come from an “in” color space of linear to an “out” colour space of sRGB