Sorry I haven't been responsive here, just either busy or dealing with headaches & lethargy, about the recent changes, there isn't a new vertex buffer, there isn't one at all now
basically before I was creating a vertex & index buffers for a (screen-space) quad the new version removes them and replaced with a single over-sized triange, the positions & uvs are constants in the vertex shader i also removed some redudant matrix transforms plus some other minor tweaks. So the changes are mainly removing buffers, removing pipeline setup and modified/simplified vertex shader.
Regarding delta-e formula that you guys having been looking at and/or testing, delta-e 2000 while the most accurate way to perceptually compare colours it is the most costly, surprised it was even usuable but i was considering it as an non-default option. I don't think you need to use this to deal with the outline issues, from what I've briefly read here it comes off like chroma spill, if that is the case you should be able to handle this seperately while using a cheaper, simpler versions of delta-e. There's like 3 or 4 standards each with more accuracy but more computationally costly.
Just search for chroma key spill, that is what I will be looking at soon.