You can add a spot color that you have measured by using a colorimeter.
Connect the colorimeter.
On the Spot Color screen, click Settings - Instrument, and then click a colorimeter.
Click New (Measurement) on the Spot Color screen.
Place the colorimeter on its white calibration plate, and then click OK.
Press the button on the colorimeter to acquire color values.
Enter Color Name and click OK.
The Spot Color screen returns. The measured color is added to the list of spot colors.
The comparison, for matching, with the names of the spot colors in the image data is performed using "Prefix + Color Name."