Mac OS X's built-in app Digital Color Meter is an extremely useful tool for me, and I love it. However, the only problem is that it is not exact.
I manually created an image with RGB values of arbitrary numbers, say (38, 205, 86) using OpenCV. I then opened up the image with Preview, and measured the color with Digital Color Meter. Unfortunately, its output was close but not exact.
I also noticed that there is an drop down menu, such as
Display in native values
Display in P3
After playing around with all of these options, I am very happy to report that the option Display in sRGB produces exact match with the pixel!