Rich black : faded gray appears colored
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.
A neutral rich black, needs to have some characteristics.
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?
A color profile is a complex algorithm
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.