St. Ursula - painting discussed

Caravaggio's discussed painting : 

The Martyrdom of St Ursula - is not finished. I came to this conclusion as I studied old masters tractates and paintings in musea, to investigate their technique for using in my own paintings. You can see clearly that St. Ursula is still in grisaille underpainting phase (!), a part of her clothes and her skin. I heard often the remark that this is symbolism since she is dying, however I want to challenge that explanation. I am convinced that this painting is just not finished because it is there in grisaille phase. Moreover, the person in her right back is quite yellow, whereas the other personages have full skin colour. This final skin colour is the result of glazing Chinese vermillion (Mercury Sulfide, a mineral) over the yellow skin in progress. This pigment was and is very expensive, thus it is logic to use this in the final phase. This supports that the theory that this painting is not finished.