Every link in your Navigation panel like the default ones Inbox, All, By Me, Requests, Spam, Settings, Trash and every stored searches and folders you have created can be color coded by hovering your mouse over the item pressing the arrow down icon and choosing "Set color".

Now when your search or watch your inbox in Wave you will get those color codes and the text of the item highlighted thus making it easier to get organized. You might add a color for private waves or one for a work project or whatever you waving alot about.