Gets the colour used for stroking: its colour space and values. Initially DeviceGray black (0).
[UnscopedRef]
public PdfColor StrokeColor { get; }
ISO 32000-2 §8.6.8, Tables 51 and 73. Set by CS SC SCN G RG K. The space is the one the operator selected; a default
colour space replaces a device space when painting (§8.6.5.6, DefaultColorSpaces).