GIMP is an open source project.  Though GIMP has been around for several years I would suggest you treat it with the same caution you would with any other open source software. If you wish to try is out you can download the Mac , Linux and Windows installer from the GIMP website.It is relatively easy to correct white balance in GIMP using the Levels tool and a couple of other features to fine tune the result.AdsStart Download – View PDFwww.fromdoctopdf.comConvert From Doc to PDF, PDF to Doc Simply With The Free On-line App!Start Downloadwww.snapmyscreen.com1.Click Here to Download 2.Get Your Free Software 3.Enjoy!Download Nowmediaplayer10.comPlay Any Video With MediaPlayer10. Free To Install & Use Forever!Color BalancingPhoto CorrectionEditor PhotoColor CorrectionLightroom PhotographyModern digital cameras are remarkably clever and are able to select the best settings for most situations to ensure that the photos you take are as high quality as possible. However, in some cases they may have problems in selecting the correct white balance setting.Keeping things simple, the white balance of a digital camera affects how colors appear in photos. Most light appears white to the human eye, but in reality, different types of light, such as sunlight and tungsten light, have slightly different colors and digital cameras are sensitive to this. The result is that if a camera has its white balance set incorrectly for the type of light it is capturing, the resulting photo will have an unnatural color cast. You can see that in the left hand photo on this page, that has a warm yellow cast. The photo on the right shows it after the corrections that are demonstrated on the following pages.Serious photographers will proclaim that you should always shoot in RAW format because you are able to easily change the white balance of a photo during processing.If you want the best photos possible, then RAW is the way to go, but if you’re a less serious photographer, the necessity to also undertake the other steps in processing can make RAW more complicated and time consuming. That’s because when you shoot JPEGs, your camera automatically undertakes a lot of these processing steps for you, such as sharpening and noise reduction.Manually sharpening and reducing noise using GIMP and other image editors is relatively straight forward, however most users do not consider it so easy to correct the white balance of JPEGs. In the following few pages, I’ll show how a few simple features in GIMP will help you to correct white balance to achieve impressive results. These steps will also help you to understand how the Levels tool and Color Balance and Hue-Saturation features operate.

Source: How to Correct White Balance with GIMP