This can be addressed with a quick and simple color balance adjustment to warm up the color tones. Using The GIMP program (free, open source and available cross-platform) simply go to the colors menu and then choose color balance. You will be greeted with which ranges to adjust and three adjustment sliders: Cyan/Red, Magenta/Green and Yellow/Blue.
For most images you don't need to do much, a simple +5 on the Cyan/Red scale and a -5 on the Yellow/Blue scale done with the Midtones option selected is just enough to do the trick.
For illustrative purposes I have an old photo taken of my old cat with my first decent digital camera, a Minolta Dimage S304. The first image is the untouched photo from the camera, followed by one done on Midtones only with a +10, 0, -10 on the scales and the last one with a +5, 0, -5 adjustment done all all three range adjustments.
|+10, 0, -10 - Midtones Only|
|+5, 0, -5 Shadows, Midtones and Highlights|
As you can see, it doesn't take much to positively change the final image. And if you are new to digital development, this is a great place to start that will improve many photos all the while not being difficult.