Transparent masks

I was wondering if there were any tutorials on tacial tracking I could use to make transparent overlays to make people blue in a video.

does this kinda helps?

Blender does not have the power to recognise the human face. You can track the features of the face, but it’s fidly: Eye’s loose their markers when they blink, mouths loose their markers when they open, everything else moves it’s markers when it feels like it. But even tracking the face will not help to recognise the the outline of the neck.

On the other hand…

How much red do you have on screen that red tones other than the skin. It may be that you can work in the compositing nodes to isolate all the red tinted stuff (skin) and tint that blue. Have a look at … maybe you can do that with pink skin ratehr than green sheet.