I’m trying to reverse engineer a graphic that I like in Illustrator, and here is the part that gives me trouble:
I have followed a few tutorials using the Grain effect with multiply, however it does not have the desired effect in my case. Here’s what I did:
The result is this: The color is correct when over transparent background, but when I move it over the desired background, it becomes darker. I suspect this is an effect of “Multiply”, where the grain is multiplied with the background color instead of simply covering it.
I guess I could try and changing the grain color until the combination matches, but that just seems wrong and inefficient. There has to be a better way. How to best achieve this?
Answer
I noticed that this is still on the ‘Unanswered’ page… So I decided to tackle it. I love figuring things out; we can do this!
I found that it’s just simple math in the end – but unfortunately Illustrator is lacking the feature we need in this case.
Here are the two colors you used (on the left):
Color 1 is the base color and Color 2 is above it. As you’ve seen, applying a Blending Mode of Multiply to these two colors gives you this resulting third color:
This clearly does not give you the result you want, so as you’ve already deduced your second color is wrong.
To “reverse engineer” two colors – where it is known that Color 2 is the result of color multiplication – just take the two final colors and do the reverse.
Here’s the math part:

(Using numerals for example) we know that 4 multiplied by 6 gives us 24

We also know that 24 divided by 6 gives us 4

(Now with colors) we know that Color 1 multiplied by Color 2 gives us Color 3

Therefore Color 3 divided by Color 2 will give us Color 1
Unfortunately for whatever reason (I don’t know) Illustrator doesn’t even have a Divide Blending Mode.
But Photoshop does…
So starting again in Photoshop now, using the two colors you want to end up with (as seen on the right in your example)… As per the example above we have Color 1 on top of Color 3:
Then change the Blending Mode of Color 1 to Divide, and the result gives us (the desired) Color 2:
A new color… This is the color you’ll want to replace Color 2 (in the first example) with…
So now beginning again with our (new) Colors 1 and 2:
By applying the Multiply Blending Mode we now get the proper outcome:
I know I’m probably too late to help Alexander but this is useful information anyway… so here it is.
Attribution
Source : Link , Question Author : Alexander Rechsteiner , Answer Author : BANG