Here is a color picker I have written lately. It has some advanced features like picking any pixel from screen, 3-block demonstration, hsl support, alpha presentation, float conversion, luminance and interp calculation, argb hex, creating random colors based on rgb, hsl, hsv spaces, so on and so forth.
It is written with native C++/Qt combination which means the program opens and operates quite fast.
There are 64 bit Windows and Linux binaries available right now but 32 bit can be compiled if requested.
It can be also compiled for MacOS with zero percent code modification but since I do not have a Mac, you have to download the IDE and compile yourself. The source code is included anyway.
The software is free which has both meanings, free as a free lemonade and free as an open-source.
Direct Download Link