2D markers that use color to encode extra bits of information do exist actually, see for example http://josephdegol.com/docs/ChromaTag_ICCV17_Paper.pdf http://j

2D markers that use color to encode extra bits of information do exist actually, see for example http://josephdegol.com/docs/ChromaTag_ICCV17_Paper.pdf http://josephdegol.com/docs/ChromaTag_ICCV17_Paper.pdf. So it's not a bad idea. But as other commenters mentioned, for this application it might not be a good fit if the researchers are limited to using black and white cameras (understandably - there's a hardware tradeoff to capturing color information in terms of speed and resolution). More generally, color information is harder to capture robustly under varying illumination conditions, not to mention the accuracy of color printing, so these color markers haven't really caught on to my knowledge.