Gpick - Advanced color picker

gpick is advanced color picker written in C++ using GTK+ toolkit

Features:
* Create palettes from images
* Color scheme creation tools
* Fast color picking
* Magnification
* Colors automatically named
o Closest color name is found using CIE94 color difference function, which is closer to the way humans interpret color differences, than difference of red, green and blue color amounts
* Export to following formats
o Inkscape/Gimp Palette (*.gpl)
o Adobe Swatch Exchange (*.ase)
o Alias/WaveFront Material (*.mtl)
* Import from following formats:
o Inkscape/Gimp Palette (*.gpl)
o Adobe Swatch Exchange (*.ase)
* Picked colors can be copied to clipboard in multiple formats
o Hexadecimal notation - #rrggbb
o Functional RGB notation - rgb(red, green, blue)
o Functional HSL notation - hsl(hue, saturation, lightness)
o Custom conversions can be done, but requires some Lua language knowledge
* Oversampling with five falloff types
o Multiple pixel values are averaged to help picking colors from sources with noise, patterns and etc, where each pixel is different and overall color is produced by different amounts of particular color
* Mix two or more colors using variable number of steps and different mixing types
* Create lightness and/or saturation variations
* Create harmonious colors
* Create color schemes

Install gpick in ubuntu
Download deb packages from here once you have deb packages you can install by double clicking on it.
Screenshot

nb:sourcecode here