You are using a color negative film. This type of film, after being developed, yields a negative image that is just a means to an end. Next this negative film is fed into a high-speed printing machine that makes positive prints on paper. This negative – positive system has great advantages in that the printing cycle affords an opportunity to correct and therefor enhance pictures that were poorly exposed when the initial picture was taken with the camera. We are talking about over and under exposure. You should know that this negative – positive method can greatly increase the yield as to the number of acceptable prints obtainable from a roll of film.
That being said, there is a limit and severely under-exposed and over-exposed negative are impossible candidates. Nevertheless photo labs (photofinishers) make their living by selling prints. Thus the tendency is to print and sell prints made from these dreadful negatives. If you were to inspect and reject these substandard prints, you would not be charged for them.
Severe under-exposure in the camera results in substandard negatives that when printed yield shadowy off-color prints. Bottom line, these negatives should never have been enclosed in your photo packet. You remedy is to better understand the operation of your camera and practice the art of making good exposures. No easy task but you are up to it.