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

[Philip Taylor]

Ross Moore wrote:

> On 25 May 2020, at 9:00 pm, Philip Taylor <P.Taylor at Hellenic-Institute.Uk <mailto:P.Taylor at Hellenic-Institute.Uk>> wrote:
>
>>
>> [UNIV: Plain XeTeX] —
>>
>> [i]t would appear that [] "xdvipdfmx" has been enhanced to support transparency, as a result of which Khaled's suggested FFFFFF00 no longer works (the text is invisible, see attached).  Could anyone tell me how, short of using \specials, I can achieve 100% white with 100% opacity (= 0% ink) in XeTeX ?
>
> I’m sorry, but this just doesn’t make any sense to me — but see further below. Surely 100% opacity means that the blend between background and foreground is 100% background, 0% foreground. Thus your text will be invisible, whatever colour has been specified; that this is white becomes irrelevant.

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.

> The only way to get 100% white, over a coloured background, would be with 100% ink, so 0% opacity.
> Any other opacity level will allow some of the background colour to be mixed in.
> At least that is how I understand what colour mixing is all about.

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.

** Phil.
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