There are many different themes that are used for ecommerce sites.  One of the most important parts of a theme is color chosen.  Some of the biggest sites on the world wide web like to use a blue themed layout.  Blue is friendly, it makes shoppers feel at ease.  Many high quality sites like this palladium rings site uses this blue theme.  Having contacted them and receiving feedback they say it works very well for them.  Their rings are a natural white color so the contrast of the white rings and the blue theme works well.
I thought this was a bit curious so I decided to look at other sites.  I found a tungsten wedding bands site that looked very professional.  It too had the blue theme although theirs had a lot more white than the palladium site.  I contacted TungstenRingsOnline.com and asked them why they decided on the blue theme.  They said it felt clean and hopefully attracted more customers.  I turned to someone that knew a lot about themes and they said in their research they have found soft colors worked best for conversion.  Unless there was a product that had a different color theme would match better.  For example this website for stair treads tied the look of wood into it.  I liked the way it looks and think it was a good idea to go with that theme.