In addition to editing the XML, as @vanepp indicated…
Most drawing/graphics programs have ability to change colors via doing things like Invert, Replace, Filter…etc.
Inkscape has several ways of doing it (see Filter>Color>Invert and Other selection/filter tools
Simple Drawing programs like Paint, PaintBrush have selectable color changing…
OpenOffice uses the panel called Color Replacer… Also has a Paint bucket…
Etc, etc… all require some learning but, are simple enough.
NOTE: The file Type does matter - resolution of SVG, PNG, JPG differ…
Below is an example using Boxy…
The process is:
•Export SVG (from Fritzing) only the Copper Fill, Traces…).
•Open the SVG (or other).
•Drag the Group of items out of the way.
•Create a Rectangle and Fill it with Black.
•Select the Group of items and change the Color of the Stroke to White.
•Drag it back to original position and set it ‘Bring to Front’
Done Now you can save/export…
