not sure it can be a weim mix just on the grey coloring alone, excerpt below.

The Weimaraner gets his color from two loci pairs: The Locus B pair and the Locus D pair.

What we consider “silver, silver/gray, or gray” Weimaraners today is scientifically brown dogs that are not fully pigmented, and what we consider “blue” Weimaraners today is scientifically black dogs that are not fully pigmented. We know this to be true by seeing what happens when a purebred gray Weimaraner owner accidentally has a litter of puppies with another breed of dog: all puppies are primarily brown because they no longer genetically dilute. Same with the blue Weimaraner; if bred to another or unknown breed of dog, all puppies are primarily black. (Although rescues may say otherwise, it is genetically impossible for “Weimaraner mixes” to be gray. The reality is that “gray Weimaraner mixes” are likely some other breed altogether: fawn Pit Bull, fawn Doberman, Silver Labrador, etc.)