Spoiler:The blue image was exported from Hard Doom.
The green one in the middle is a basic recoloring of the blue image (with hue variation).
I tried to add transparency in the third image to see the difference (but there is not, it applies the same with the blue image).
So it seems at a first glance that image 1 & 2 are of the same nature.
However, when I import both images in Slade3, the blank around the torch doesn't disappear on the green image, while the blue one does.
I expect this to be a novice mistake, but I would be grateful if someone could provide a solution.