Gets the colour space of the samples; null for an image mask, for a JPEG 2000 image without one (see
ResolveColorSpace(DecodedImage)), and when it is missing or unusable.
public PdfColorSpace? ColorSpace { get; }
ISO 32000-2 §8.9.5.1, Table 87 (any space but Pattern), §8.9.7 for inline images (abbreviated and resource names), §11.6.5.2 for a soft mask (DeviceGray).