This is such an interesting topic, I just took a trip to Paris and Stockholm and the thing that stressed me out the most was finding shoes that were comfortable enough to walk a lot but not be my white tennis shoes. Well, I tried several pairs and nothing worked, so I ended up wearing the white sneakers, and it was funny, it didn't matter one bit.
Other people in Paris had white sneakers on and if they "knew" I was an American by wearing those, oh well. We walked a lot, and I wouldn't have made it without the white sneakers. I did take a pair of sandals for a nice dinner out.