Hello Silentknight,
We apologize for the inconvenience caused, as per the description above, you are not able to turn off Grayscale Printing in Adobe Reader, Is that correct?
Make sure that you have unchecked the option "Print in grayscale" from the Advanced Print dialog box and make sure that from the main Print dialog box>Advanced>Output>Color, GrayscaleComposite Gray is not selected.
These options are printer properties, so you might have to look in Advanced Properties of the printer.
If you still experience the issue, please refer the Adobe Reader's Preferences and reboot the machine, to reset the Preferences, please refer to the steps mentioned in the article How to reset Acrobat Preference settings to default.
What is the make and model of the printer installed and the version of the driver/firmware installed?
Is it a Mac or Windows machine?
What is the dot version of Adobe Reader installed? To identify, refer to Identify the product and its version for Acrobat and Reader DC
Let us know how it goes and share your findings.
Regards,
Anand Sri.