SO, I had a similar situation happen to my Crystal white pearl Mazda SUV 2 years ago. This ISSUE here, is not the paint code or the prep work. The body shop "might" have done everything acording to spec. This issue here, is the actual MATCHING of the new paint to the color on your car. This is where the voodoo science and skills comes in. The bodyshop need to take the TIME and have the SKILLS to actually take the original paint code and color match it to the paint on your car. Most shops just take a easy way out and paint to the original color.
2011 M3 Sedan DCT ZCP
2003 540i M-Sports Pkg, Dinan (retired)