There are two ways to look at the shelving you use and your decor. The first is that you can buy retail shelving that simply "blends in," in that it is unobtrusive and not noticed.
The second is that you can buy retail shelving that complements your decor and is in fact a stylish asset in and of itself. It may provide a counterpoint to subtle, sedate decor, for example, by being bright when it is bought in a bright contrasting color that provides some pop.
The interesting thing is that either one of these approaches will work. While your customers will certainly notice your store's shelving if it complements rather than blends into your decor, they will notice your merchandise even more if it is placed on a particularly visible fixture or shelf. The key is simply to do what works for your particular situation. If attractive or contrasting fixtures will make your merchandise more visible in that it will draw customers' eyes to it, then it will work.
Certain types of merchandise, like clothing or jewelry, can really stand out if you provide some focal lighting on the display. The customers won't notice the shelving itself; they will simply notice the merchandise that is literally in the spotlight, and take it from there.
As stated in the first paragraph, you certainly don't want your retail shelving to be shabby, chipped, in disrepair, or otherwise in need of replacement. While the colors, materials and styles of retail shelving you choose are certainly important to product displays, what's most important is that the shelving itself is in good condition. Make sure to replace shelving whenever it begins to look shabby, even if it is in good condition otherwise, to make your displays are most effective.
It is also a good idea to update fixtures and shelving whenever your store begins to look dated. Today's retail shelving choices are many, and you can choose from a variety of colors, styles and materials based upon what you need. If you can't afford to replace your entire stock of retail shelving, start with a few pieces that will complement what you already have, and build as you go.
It won't do to use a gigantic shelving unit for a small display, or delicate slatwall shelving for a heavy, large display. Choose your shelving and fixtures so that they fit the displays in question. If you don't, your customers will be focusing on how rickety the shelving looks, or how the extra space in your display overwhelms or swallows up the small products shown.
In short, make sure the shelving you choose fits the merchandise on display. If your shelving is shabby, out of date, the wrong color or material, not lit well when it should be, or of the wrong size or type, you may find your customers focusing on your shelving rather than your merchandise. These fixes should take care of that problem, so that your customers are focusing on your merchandise, as they should be.