Gets or sets the colour of the item's text (C, PDF 1.4); black when absent or not three numbers, components clamped to 0 to 1.
public PdfRgbColor Color { get; set; }
ISO 32000-2 §12.3.3, Table 151: DeviceRGB, default [0.0 0.0 0.0]. Setting black removes C, the default; any other
colour is written as three numbers (PDF 1.4), and a later save of a document below PDF 1.4 raises it to 1.4.