Check your White Balance. This is a setting that adapts the color rendering of the camera to the ambient light. For example, if you'd take pictures indoor under "warm white" artificial lighting the pics would all look yellow if your white balance were set for daylight. Vice versa, if you have your white balance set for indoor lighting and take pictures in outdoors daylight or with flash, the pics will come out with a blue tinge.
To set the camera's white balance, press the WB button and use the control dial to select the type of white balance according to the ambient light, then press the MENU/SET button. For more detailed info, see p.44 of the camera's basic user manual.
If you don't want to be bothered with have to set the white balance manually each time the lighting changes, set it to AWB (Automatic White Balance). This way, the camera itself guesses the type of lighting for each picture, and this usually works well.