There are some rumors that white, blue and liver dogs will have a higher occurrence of health problems such as HD, ED and DM. However these rumors are unfounded and based on misconceptions and incorrect information. While these colors are undesirable according to the GSD standard, these dogs are no more likely to have these health problems than the other correct colors are.
There is a known health issue in some other breeds called Canine Color Dilution Alopecia, which causes blues and other dilute colors to have a skin condition called alopecia. There is some controversy as to whether this affects blue German Shepherds or not. Most of the research does not list GSDs as one of the main breeds affected, but does indicate that it is possible.
Many health issues in the German Shepherd are genetic and can be passed on generation after generation, sometimes even hiding recessively for several generations. You are going to find more health issues pop up in poorly bred lines from irresponsible breeders. You will not find a good breeder using blues, livers or panda colored dogs in their breeding program. Because of the irresponsible breeding practices of those who do purposely breed these faulty colors, you may find more health issues in these dogs. Again, that is due to poor breeding practices, not due to the color itself.
When breeding, breeders should never breed for specific colors. As when someone concentrates on producing dogs of certain color, they overlook other more important traits such as health and temperament. If you come across a breeder that is selecting for color or purposely producing faulty colors (such as blue, liver and/or panda), this should raise a red flag for you and you should look elsewhere.
If you are determined to purchase a blue or liver dog, these colors can pop up in well bred litters. It does not happen often, but because it is a recessive gene, it does happen occasionally. Your best bet is to get the word out among good breeders and let them know that you are looking for a blue/liver puppy. It may take awhile, but eventually when one pops up the breeders will know who to contact. Networking has become very helpful when it comes to connecting good buyers with good breeders.
Or you can simply recognize the disqualifying colors for what they are and purchase a well bred standard color puppy. If you purchase your puppy from an irresponsible backyard breeder, then yes, you will be more likely to encounter health issues.