I have a question about using rich black for a print document. In InDesign, I set a rich black color for the background (0/80/0/100), and I need to set a faded round gray shape, with an opacity around 30-40%, on top of the black background. I create this shape in Photoshop and import the PSD file in InDesign.
Issue : as the rich black contains Magenta, and the gray has transparency on top of it, it appears colored (because of the Magenta in the mix).
Is there a solution to make the gray actually gray on top of my rich black background ?
Thank you very much !
I don't know why you choose that rich black combination in the first place. You probably don't want a neutral gray but a warm red.
Also, when doing a print job you can simply use the values of the colors you expect, not a transparency which, depending on the ink and blending modes you use, throw different results.
1) The added colors besides the black, need to give a neutral gray. That seems obvious. In this case if you remove the black it is clear you dont have any neutral grey.
2) In a neutral CMY gray you will find simmilar values of magenta and yellow (red), but you will find more cyan. This is becouse you have 2 inks to neutralize with one.
For example. In the rich black resulted of aplying the Swop color profile, gives you C75M68Y67K90. See how you have more cyan?
If you have some color gradients in rgb and you convert them into a cmyk file you don't have linear conversions. The first darkening of a tone is performed by a complementary color. After some point the black ink comes into play, not in a linear way either.
This algorithm (and resulted cmyk values) also depends on what paper you are using for printing.
You can read some explanations here: http://otake.com.mx/Apuntes/RGB-CMYK/RGB-CMYK-5.htm It is in spanish, but you can use google translate.
1) Make your gradient in rgb and convert it after to cmyk using the correct profile.
2) Make a rgb gradient as a test. Extract the values of the neutral gray you need, and make a gradient using thoose values, at least for the CMY part and play with the black as you like.
Don't go beyond the total ink your profile is recomending.