For example, I have rect:
<rect fill-opacity="0" height="10" stroke="#000000" stroke-width="3" width="10" x="0" y="0"/>
Although fill color is not specified, "fill-opacity" is set to 0 - rect should be transparent. But as long as "fill" is not specified, SVGParser sets fill color to opaque black.
Code from SVGParser:
guard var fillColor = styleParts["fill"] else {
return Color.black
}