iMac display RGB values Why does the iMac display show non-zero values for blue and green pixels for a .png image whose blue and green color planes are zero?  I used the digital color meter to show the non-zero values for the blue and green pixels and I confirmed that the .png file has zero values in the blue and green color planes by using python scripts to inspect the array values.
You might check the iMac's monitor calibration settings.


  System Preferences > Displays > Color > Calibrate...


or choose one of the other Display profiles. Which Digital Colour Meter are you using?  It probably must be also calibrated in sync with the above setting...