[XeTeX] XeTeX, colour, \special, \shipout

[Philip Taylor]

Ross Moore wrote:

> Hi Philip.
>
>> On 20 Jun 2020, at 12:08 am, Philip Taylor 
>> <P.Taylor at Hellenic-Institute.Uk 
>> <mailto:P.Taylor at Hellenic-Institute.Uk>> wrote:
>>
>> XeTeX does what is expected if one uses \special {background cmyk 
>> 0.83 0.82 0.21 0.60} and ships out pages in the normal way; however, 
>> if \shipout is invoked directly, the shipped out boxes have a 
>> transparent ground.  How should the background colour of boxes which 
>> will be shipped out directly be specified ?
>
> You need to understand that “background color” is *not* a basic 
> concept in the PDF graphics model.
>
> see the discussion at this link (and elsewhere), as shown in the image 
> below:
> https://community.adobe.com/t5/acrobat/change-background-color-of-pdf-pages/td-p/8476774?page=1

OK, thank you for that information Ross.  Clearly I was unaware of that, 
but the discussion was not particularly helpful, especially those who 
advocated using the Adobe Reader/Acrobat GUI to change the colour-scheme 
to "accessible" !  But in most ways I am no wiser — I have still have no 
idea why \special {background cmyk c.c m.m y.y k.k} can change the 
colour of pages shipped out from the output routine but not via a direct 
shipout.  It is not as if \special {background cmyk c.c m.m y.y k.k} is 
inserted as a part of the output routine — it is in mainline code.  So, 
why does it affect only pages that pass through the output routine ?

** Phil.
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