I've been asked to key out a very rough video of a person dancing in front of a green screen. However
due to the poor lighting conditions and the dancer being dressed in a blue t-shirt, I'm losing the upper part of their body.
Does anyone know if it is possible to key back in a colour?
to try and better isolate the color rage that you need to key, you should try to use a junk matte, which could be as simple as keyframing a mask that follows the dancer. the tighter the mask is to the dancer, then more narrow the color range is that need to be keyed, and that can help keep the data that you don't want to key out.
also, there is a good tutorial for using auto-trace to create the junk matte here: