Many clients come in holding a reference sweater and say: I want exactly this.
I understand the request. But what I tell them is this — that sweater is a result, not a production spec. The final hand-feel of a sweater is determined by yarn composition, machine gauge, washing, and workmanship — all working together. The sample in your hand does give me a useful silhouette reference, and to some extent, it makes it easier for us to deconstruct its construction.
So what we do is get close. Color can be custom-dyed. Hand-feel can be tuned through washing. The sample is the starting point. Together, we decide where the finish line is.