Without a grayscale space there's no way to get a color managed conversion to grayscale inside of ID. With AppleScript I can go get the conversion from Photoshop. This takes the RGB fill of the current selection and gets the grayscale conversion in PS based on the current PS Color Settings: tell application "Adobe InDesign CS5.5" activate set {a, b, c} to color value of fill color of selection tell application "Adobe Photoshop CS5" set theColor to {class:RGB color, red:a, green:b, blue:c} set gs to convert color theColor to grayscale set k to gray value of gs end tell set properties of fill color of selection to {space:CMYK, color value:{0, 0, 0, k}} display dialog "CMYK 0|0|0|" & k end tell Don't know if you can do something similar with JavaScript edit: I added a line to update the selection fill with the converted CMYK color
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