Whatever the shape, their role is to create interest, appeal and even reflect the restaurant's personality. All the plates I use are white. It also takes away from the food. While chefs are divided on the virtues of the squeeze bottle to garnish with designs, most agree it is useful if the ingredient makes sense. A colorful vinaigrette might serve as the acid to enliven flavors or a basil oil might provide contrast.
Reduced vinegars work well.
I want every dish to taste and look the same. Therefore, the dishes are styled so there is no room for individual interpretation. That is how I build consistency. Chefs caution the over enthusiastic. When the urge to garnish strikes, beat it back and remember that less is more, they say.