This online tool assists you in mixing and matching various Apple Watch band styles - to give you an idea about how it'll will look according to your taste before you buy the product and the bands.
I wanted to see what kinds of bands look good on an Apple Watch Series 4 Space Grey, so that I can keep a collection when I have my hands-on the smart watch. My search string literally was 'bands that go with black apple watch' and it led me to MixYourWatch site.