Clarify ColorSpace for 3D Data Streams

[lrosenthol]

Table 311, entry ColorSpace

The RGB colour space in which the 3D artwork’s colour values are encoded. Valid values are the name DeviceRGB, an array specifying a valid CalRGB color space (see 8.6.5.3 "CalRGB colour spaces"), or an array specifying a valid RGB-based ICCBased color space (see 8.6.5.5 "ICCBased colour spaces"). If this key is not present, the colour space for the 3D artwork colour values are considered undefined and a PDF processor may choose any appropriate RGB-based colour space, such as sRGB.

It is not clear from other parts of the text whether a DefaultRGB present on the page where the Annotation referencing the stream is used, should be used "in place" of the DeviceRGB (as would be the case for other uses of DeviceRGB). I believe that it should.

[petervwyatt]

Proposed solution: add a new 2nd sentence:

If the name is DeviceRGB and the page where the annotation referencing the 3D stream is used has a DefaultRGB color space, then the DefaultRGB color space shall be used (see 8.6.5.6 Default colour spaces).

[petervwyatt]

PDF TWG also identified typo "If this key is not present, the colour space for the 3D artwork colour values are considered undefined..." --> "... is considered..."

[lrosenthol]

This is also related to #34