But, since that application is based on my Web browser, in a way I'm a bit restricted, by default. For instance, if you work with images a lot, then a web browser based color picker is not the one for you. In that case, if you're looking for a dedicated app that's written in GTK+ toolkit which has the ability to pick colors from images to export/import color pallets from other popular graphic suits, etc ... then Gpick is an excellent utility!.
*. Magnify images for easy color picking.
*. Create color pallets and import/export.
*. Supports pallets created by various other formats such as - Inkspace/Gimp, Adobe Swatch Exchange, Alias/Wave front format, etc.
*. Save/Read in HTML, RGB, HEX, HSB / HSV, and HSL.
*. Send to system-tray so you can easily access it when needed.
And also, once you select a color, Gpick automatically lets you see similar colors that goes with it as well. So, if you use Ubuntu 11.04 Natty Narwhal, 10.10 or 10.04, then you can install Gpick by using the below command in your Terminal.
sudo apt-get install gpick