One of the first lessons you learn when you graduate from taking snapshots to taking photographs is that cameras don't see the world the way our eyes do. The difference between our view of the world and our camera's view can be frustrating at first.
Color temperature is one of the ways that our camera sees the world that we often don't notice, and it is the primary reason that your indoor photos come out looking yellow. The color temperature coming from light bulbs is what causes a color cast.
Do yourself a favor. If color temperature is unfamiliar to you, take a trip to the Home Depot or some other hardware store. With the end of incandescent bulbs, you can usually find a display demonstrating the light coming off of the new CFL and LED lightbulbs. The display gives an excellent side-by-side comparison of different color temperatures. When looking directly at the differences, you should easily notice that some of the light bulbs produce a yellowish light, others produce a more bluish light. This is color temperature in action.
Color temperature is measured in Kelvin. A daylight bulb is around 5000 kelvin, and an incandescent bulb (the most common type of lightbulb in homes) is around 2600 kelvin.
But you don't really need to worry much about that to start. What you do need to know is that there are warm tones and cool tones. Your camera measures color temperature using the white balance. Most of the time, your camera is set to Auto White Balance (AWB) and makes its own decisions about the color temperature of your subject. If the camera thinks the color temperature is the same as daylight, but you are actually getting indoor light, the photo will often come out too warm. The result will be a yellow looking photo.
Normally, a camera is excellent at choosing the correct white balance for the lighting conditions, but in a home, cameras have mixed light sources. All homes have windows, which bring in daylight balanced light for most of the day. So if you take a picture of someone indoors, the camera sees the warm light from the lightbulb and the neutral light from the window, and it usually picks the color temperature from the window to control the white balance (since it is far brighter than a lightbulb).
Fortunately, there are multiple ways to correct this.
Shoot with the right color temperature
You can set the white balance in camera before you shoot. The technically correct way to do this is to set your white balance manually using a white or neutral gray card. A large one can be picked up for around $10 (one side white and one side gray). You will have to read your manual to determine how to navigate to the correct menu for Custom White Balance and also to understand the process to set the white balance. Whatever the process, it's important that the card is placed in the same light as your intended subject.
Another option is to set the white balance using one of the camera's pre-determined settings. These include settings like incandescent, tungsten, and florescent for indoor lighting. Tungsten was the filament used in incandescent light bulbs and the color temperature it emits often results in the yellow color cast in photos. Since many of the new light bulbs have the same color temperature they will cause the same problems.
Setting your camera to incandescent or tungsten will help eliminate this problem. The florescent setting is used with florescent lights which have their own color cast issues. Many point and shoot cameras have a color temperature setting like I mentioned above, so it is a widely available fix for color cast issues.
Fix RAW photos in Post
This is my preferred method of handling White Balance but it assumes you are shooting in RAW and that your camera handles white balance fairly well. In most cases, shooting in RAW allows you to fix a multitude of problems in post, and White Balance is one of the handiest. If you are using a program like Lightroom, you can set the White Balance to a particular color temperature, or use one of the pre-determined settings I mentioned above. If your photo is too yellow, slide the temperature a bit to the left. If it gets too blue, slide it back to the right. Lightroom also has an eye dropper tool next to the color temperature slider (other programs do as well). If you have a neutral gray color in your photo, or if you took a photo with a gray card as I mentioned earlier, you can place the eyedropper on that gray area and click. This will set the photo to the appropriate white balance. You will then want to sync that white balance setting to the rest of the photos taken at that time.
Fixing Jpegs in post
If you are not shooting in RAW, there is still an option to change your white balance. Even in the basic editing programs that come with your OS, there is usually an option to adjust temperature. You will want to remember to adjust the temperature down if your photo is too yellow. However, I've found that jpegs with a color cast are difficult to get right if I only adjust the temperature (iPhone photos struggle with this problem).
For jpegs with a color cast, my best results have been from using the color dropper on a neutral gray area of the photo. Using a gray card at the beginning helps in these scenarios. If I don't have a gray color, I like to use the Auto color setting, then tweak the temperature up (if it comes out too blue) or down (if it turns out too yellow).
If you don't like to shoot in RAW, or to do a lot of work in post, you will have to anticipate color temperature issues. If you know you will be indoors and working in ambient light, a little bit of anticipation can save a headache later.