Color Grading

Color Grading plug-in, creates a cine image look based on user input. For a
contemporary image look, use complimentary colors in shadows and
highlights. It is also preferable to be used on a somewhat neutral image
(ie pre white balanced) for best control of the final result. If it's
not a raw image balance it before with Color Balance 2 [ http://www.registry.gimp.org/node/24589 ].

See samples:
Original:

After Color Grading filter:

Color Wheel UI tab:

Levels information tab:

Profiles tab:

Sample 2, Original:

Sample 2, After Color Grading filter:

WINDOWS USERS:
Python installation: python ships with GIMP 2.8

Copy .py and .png files in:

LINUX USERS:
Python installation:
Python usually ships with the OS so no manual installation is needed.

Copy .py and .png files in:
/home/[USER]/.gimp-2.8/plug-ins
Check if the file is marked as executable.
NOTE: Developer version generates the colorwheel if .png is not found, requires numpy installed.

In GIMP you will find it under the filters menu.

New in Version: 1.5.3
> Information pane now shows both 0-255 and percentage values
New in Version: 1.5.2
> GIMP 2.8 compatibility fixes
> Code cleaning
New in Version: 1.5:
> Channel Levels Information for applying the corrections in another program
> Profiles
New in Version: 1.4:
> Major engine refactoring
> Speed improvement
New in Version: 1.3:
> Now Double version slider/colorwheel availability, new interface like professional tools
> Midtones bugfix
New in Version 1.2:
> Saturation added.
New in Version 1.1:
> Levels added.

A nice tutorial about color grading can be found here:
http://vimeo.com/5298634

Kuler color pickers:
http://kuler.adobe.com/#create/fromacolor