Why am I getting a colour variation on screen when using the "Darken" mode in the transparency field. See attached screenshot. The "Substrate" spot colour has the "Darken" applied which is layered on top of the colour wedges. Should the colours of the wedges not display the same irrespective of whether "Overprint Preview" is on or off? P.S. I've tried the "Multiply" function as well but there is still a variation in colour albeit not as bad as the "Darken".
I suppose the underlying colors are a neutral grey? I cannot reproduce that, there is a slight variation with Overprint on and off, but not a color shift.
When working with Spot Colors one should stick, in my opinion, to managing Overprinting with »Overprint …« (in the Attributes Panel) instead of using Blend Modes.
Darken separates the spot in the same way as Overprint and has the advantage that pdf viewers that don't support Overprint (like Apple Preview and the preview in this forum) show the expected preview. Darken also gives a better result when the spot has to be converted to process colors.
Your reasoning is correct. As a Prepress house, our Pdf files we send out for approval are Press ready files, meaning that they are colour separated correctly. We have dozens of clients with different viewing software, thus creating the Preview dilemma you mentioned. We have found in the past that the "Darken" mode worked well for us up until recently when I encountered the colour variation as mentioned in my intial enquiry. Find attached a sample illustrator file showing the difference between Overprint, Darken and Multiply with Spot colours.
P.S. We avoid "Multiply" because it changes the values of the underlying colours.
Thanks for sharing, it is indeed a preview problem.
The file separates fine and when Overprint preview is turned on the preview looks fine.
With Overprint Preview off the preview problem becomes visible.
It is not only Illustrator, in Acrobat the file looks fine when Overprint Preview is active but when it is turned off in the preferences, it has the same problem as Illustrator. So at least it is consistent.
It seems to be shared preview code between multiple Adobe applications (InDesign included).
I am not sure where to report this, the Acrobat Uservoice or Illustrator Uservoice, maybe both:
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