You answered my question, I thank you for your attention.
Inkscape can be a tool to change the vector graphic color, but can also be used “Developper tools” from Google Chrome to edit the color of each component vector of the image SVG … but change the vector color does not solve the problem.
I think that I did not properly formulated this question considering that this is a vector image and I might not get me adequately express in English; I apologize.
I try to better explain the problem …
The Fritzing can generate a set of vectorial SVG graphics for the production of PCBs, among which is especially important _xxx__etch_copper_bottom_mirror.svg graphic to “print” the botton layer.
The graph of this SVG layer containing the vectors in the proper format for PCBs but not appropriate to generate the gcode used by a CNC, that is, this graph would have to have the “inverted” vectors in the image: the vectors should be present where the image is white.
The CNC “cuts” where there is a vector in the image.
In _xxx__etch_copper_bottom_mirror.svg graphic, cut where it is black, where we do not want to cut. In this case we want to cut which is white but white is just the image background, is not a vector.
The question is how to generate “negative” vector of _xxx__etch_copper_bottom_mirror.svg image, ie, vectors forming where the image content is white.
(Note: although I do not believe that the CNC is the best way to produce a PCB, I assembled a CNC to study and would like to try this process.)