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I opened a new document in Adobe Illustrator CS5, which defaults to CMYK as a color mode. I imported a raster image, used LiveTrace with 6 grayscale colors, expanded, and saved as SVG, which changed the color mode to RGB (which I believe makes no difference, since it's only grayscale colors at this point). In the text, I replaced black in the plain text of the SVG to one web color and gray with a tint of that web color, where the opacity is proportional to the amount of gray. In the example below, I used 7B68EE for MediumSlateBlue. I copied the design in the SVG file with 7B68EE into a CMYK document and the color became 666699.

Here are two images of the difference for this case. The SVG with fill="#7B68EE" in the plain text:

Design with tints of 6666FF in an RGB document

The design pasted into a CMYK document:

Design with tints of 666699 in a CMYK document

A similar replacement happened from Orange (FF8C00) to FF9900 and from LimeGreen (32CD32) to 66CC33. I wonder if it's a coincidence that the hexadecimal characters in Illustrator's colors are doubled, e.g. 323232 becomes 333333.

I am using macOS Mojave 10.14.6 and Illustrator CS5 15.1.0 (yes, I really am, I was able to make them play nicely).

Why does Illustrator change MediumSlateBlue (7B68EE) in an RGB document to 666699 in a CMYK document?

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    It is unclear.. are you working in RGB or CMYK mode? Are you trying to match RGB colors in a CMYK document? – Scott Dec 15 '19 at 21:11
  • And are you really running AI CS5 with Mac OS 10.14? Those are incompatible. CS5 stopped working correctly at anything above OS 10.7. CS5 won't install or launch in OS 10.10... so.... – Scott Dec 15 '19 at 21:42
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    Well, first of all check that you are working with RGB colors before saving as SVG, because SVG is an image format for web and it will change the colors automatically. Then check that you are exporting with the same Color Settings (don't know if you using "Adobe RGB 1998", then it has to stay the same) – Soul Eeater Dec 15 '19 at 22:37
  • @Scott I updated the question with details on color modes. Yes, I am running AI CS5 on macOS Mojave, which I also added in the question. I was able to install and run AI and Photoshop CS5 up to Mojave; AI works OK but Photoshop does not. Installation of CS5 fails on Catalina. – miguelmorin Dec 16 '19 at 17:24
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    Basically, the RGB color gamut is larger than CMYK. RGB colors can be both brighter, darker, and have a wider range of hues. Some RGB colors look fine when converted to CMYK if they happen to fall within the CMYK gamut. Other colors, like the highly luminous purple in your image, are not possible in CMYK. – 13ruce Dec 16 '19 at 20:39
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Hex values are RGB colors. You are essentially asking why an RGB color is not matching in CMYK.

I copied the design in the SVG file with 7B68EE into a CMYK document and the color became 666699.

CMYK colors will often not match RGB colors. If you need CMYK colors, you basically can't use hexadecimal color definitions. Or you need to be prepared to adjust the CMYK using CMYK values, not hex values. Never use any hex value if you are seeking a CMYK color. Start with the hex for "closest possible" then adjust the CMYK values to better match any RGB color.

Possibly helpful, if not a duplicate: Mismatched CMYK Values

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  • I split the question into two so it can be a duplicate (here's the other about the color picker mismatch). I think the other thread is slightly different in that I did not understand the difference in the gamuts of CMYK and RGB and the other thread used an online converter and suggests a great method for picking close colors, but I leave it to your judgment to close as a duplicate. – miguelmorin Dec 17 '19 at 7:54

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