Color differences after recieving a poster from printing

Question

I have designed an A0 poster with Adobe InDesign. It contained a collage of different pictures. Since there was a specific part of the scene I wanted to cover for this version, I put a rectangle using the "Eye Dropper" tool to copy the background color.

At first sight, the area looked completely homogeneous. Moreover, after exporting the file in PDF format, I check the color again using Inkscape, not detecting any difference in CMYK values. Nevertheless, when I received the poster from the printing workshop, I realized that the rectangle was not integrated in the design, being of a slightly different color than the background.

What could have went wrong? How could I prevent this kind of issues in future works? I have checked the PDF with Adobe Acrobat Pro "Print Production Preview" option, but the CMYK value is the same either in the rectangle or in its surroundings.

Thank you very much in advance.

Answer 1

• The Eyedropper tool gets the colors in RGB mode if the image is an EPS. What I usually do is to get the color using the Eyedropper tool and immediately create a New Swatch and transform it to CMYK mode. If necessary move the values to match the image color.

• Another way is opening the original image in Photoshop, use the Photoshop Eyedropper Tool and click the color. Click the front color from the Tools Palette to see the Color Picker and get the CMYK values. Go to Indesign and make a new CMYK swatch with those values.