Returns the colour space of an inline image's ColorSpace (or CS) entry.
public PdfColorSpace GetInlineImageColorSpace(CosObject colorSpace)
The entry's value, such as from ToCosObject().
ISO 32000-2 §8.9.7, Tables 91 and 92: the abbreviations G, RGB, CMYK and I (Indexed, whose base may be abbreviated and whose
lookup table is a string) are allowed, and the full device names; G, RGB, CMYK and the device names never refer to resources,
any other name is a key of the ColorSpace subdictionary of the current resources (PDF 1.2).