Almost. A bug, which has been reported to Apple, prevents Hex Color Picker from reading or writing its settings when used in certain, "sandboxed" applications. (Mostly system-provided applications like TextEdit and Preview are "sandboxed". Photoshop, Illustrator and Coda have no issues with this, for example.)
Additionally, during installation, getting to the Library folder in your home folder requires holding down the option/alt key and choosing Library from the Go menu, as the folder itself is hidden from view within the home folder.
Except for this, there are no known bugs or issues and Hex Color Picker should work fine.
Web designers and programmers who need to specify colors must use a special code. This code can amazingly in this day and age not be found directly within the Mac OS X color panel. Launching other applications just to calculate it is tiresome and unnecessary.
Hex Color Picker puts an extra tab in the system-wide color panel. Instantly see the hex color code for any color, and edit it just the same with a number of shorthands.
Hex Color Picker has some shorthands for entering the hex color code quicker - deductions for the full 6 digit string from 1, 2 and 3 digits alone, knowledge of HTML/CSS color keywords (like orange, hotpink or chartreuse) and live preview of the color as you enter its code. You can also tell it whether you'd like upper case or lower case letters.
There's no change in actual functionality.