[XeTeX] \font "<platform font>":color=FFFFFF produces black, not white glyphs \font "<platform font>":color=FFFFFF produces black, not white glyphs, re-visited

[Jonathan Kew]

On 26/05/2020 23:32, Ross Moore wrote:
> Hi Phil,
>
>> On 26 May 2020, at 5:12 pm, Philip Taylor 
>> <P.Taylor at Hellenic-Institute.Uk 
>> <mailto:P.Taylor at Hellenic-Institute.Uk>> wrote:
>>
>> Ross Moore wrote:
>>
>>> I’m sorry, but this just doesn’t make any sense to me — but see 
>>> further below.
>
>> No, the fourth couplet is TT, where T is "Transparency". 
>> Unfortunately , it is a misnomer, since 00 = completely transparent 
>> and FE is almost opaque, which is why I spoke of "opacity" rather 
>> than transparency.  Unfortunately FF is /not/ opaque when preceded by 
>> FFFFFF, because the driver treats FFFFFF [FF] specially.
>
> As I said, it didn’t make sense to me.  :-)
> Thanks for the clarification, and sorry for my added noise.
>
>
>> First it is important to realise that both flattening and conversion 
>> to CMKY will take place (the document is for digital printing).  When 
>> flattening takes place, RGB FFFFFF text will completely obscure the 
>> ground, and after conversion to CMYK there will then be no ink where 
>> the text occurs. Unfortunately as things are at the moment, there 
>> will be 1/256 bleed-through of the ground because the RGB white was 
>> not perfectly opaque.
>>
>> "knockout", tho' interesting, should not be needed.  The example 
>> earlier sent shews that one can get very close to 100% white (and of 
>> course there are no white inks involved) but not to 100% and this is 
>> what I would like to achieve (and which should, IMHO, be 
>> achievable).  Were it not for the fact that the driver treats FFFFFF 
>> and FFFFFFFF specially, there would be no problem at all in achieving 
>> my aim.
>
> It looks like Akira has done what you wanted, so the exercise was a 
> success. :-)
>

What's unclear to me -- because I don't remember, if I ever knew -- is 
quite why the driver wanted to treat FFFFFF(FF) specially, and therefore 
what the implications of removing that behavior might be. Does this 
mean, for example, that text will no longer respect colors set via other 
methods such as color \specials, because the font will be considered to 
have an inherent white color?

JK