I've had self blues for at least 5 or 6 years now, originally purchased from a VERY reliable Texas breeder; maybe the same person yours are from. Mine always hatched with a very faint striped pattern on the backs, similar to yours, but lighter. Unfortunately, there are many "self blues" out there that are actually dilute splashes, mistakenly believed to be self blues when they originally started hatching, as they were a very even, light blue color. Many, many of those have been sold and shipped all over. When bred with the actual self blues, they will not produce pure self blue chicks, but if bred back to the actual self blue parent, will produce about half pure self blues. I actually purchased one of those chicks (in person, at a different breeder's barn and at a fairly large price) myself, 'though I was pretty sure she was a dilute splash. Beautiful bird, but definitely dilute splash. Splash bred to splash for several generations will produce lighter and lighter chicks that are easily mistaken for self blues. Self blue is not a naturally occurring color in silkies, and that color gene was introduced many generations ago from another breed of chicken. Without that actual color gene, it is very, very unlikely or impossible to produce an actual self blue silkie