It's worth pointing out that they have a proprietary engine and that there's no reason you cant store multiple vertex color sets in a model so they probably just do that for simplicity's sake. This is also what the slides suggest they did so I think it's a safe bet. The simplest option if you only have 4 channels is to do…
youi're missing white so it's 8 by that logic however.. if you use vertex color in most engines (eg. unreal) it's a fixed cost - you don't save anything by using only 2 channels because the data is stored as a vec4. At worst you have 8-bit precision - giving you a potential total of 1024 unique 1 bit masks. I've shipped a…