When displayed on the Macbook Pro screen it registered as one colour. On my Dell monitor it registered as something slightly different. When I used that the colour in CSS, the colour rendered differently to the original image, and DigitalColor Meter reported that there were different values between different browsers (Chrome and Safari) and different screens.
And none of these visually matched the colour of the original image on either monitor.
Not sure if it was gamma adjustment, colour calibration, drivers, graphics cards... in the end I gave up and did the best I could.
I'm not sure why you'd want to buy a utility that replicates already built-in software, but one great value-add point would be to disentangle all of this nonsense.