From Shopnix Help
After selecting a theme for your store, you can further customize the look and feel of the store by changing the color scheme of your store. Changing a color scheme sets different color combinations for the elements of the store such as the menus, grids, background elements etc.,
Below we have applied 2 different color schemes on the same store. You can choose a color scheme that goes well with your products. Example for organic foods a cool green combination is suitable while for electronics a snazzy silver combination is better.