The single most important part of your uniform is your footware. Safety first! Usually you have to provide your own and it is critical to have restaurant work shoes. Your shoes will protect you from slipping, spills, and standing.
Slipping: The number one cause of injury in any work place, not just restaurants, is slips and falls. The restaurant is one of the most dangerous places to have bad shoes. The floors of a restaurant although may be textured tile, once they are covered in a thin layer of oil they become incredibly slick. Similarly on a wet walk-in cooler or ice on the ground in the freezer, the surface we walk on is very slippery. If you've ever accidentally emptied a fryer onto the floor or tried to fill a fryer without closing the drain valve first you will know how slick the floors can get.
Many restaurants have mats down to prevent fatigue and makes slips much less likely, but even still it is very dangerous to not have slip resistant shoes. In a typical restaurant everything is made from hard solid stainless steel with sharp corners, if you fell from standing height on to the edge of a grill or prep table and hit your face or head it would be excruciating. Slipping is very real and very dangerous. You may think your tennis shoes are slip resistant and you'll be fine or you may want to look cool in your red Converse All Stars, but these are horrible shoes for restaurant work!
Spills: Restaurant work shoes typically need to be closed toe, it would be bad to spill hot soup or a pan of bleach on your foot! Sandals in a restaurant are just a bad idea. There is ice flying around, dishes fall, water gets sloshed, drains get clogged, toilets get clogged, you want your shoes water (and pasta sauce) resistant. You will want to be able to spray your shoes off to get the alfredo off of them too. There is nothing worse than getting to work early for a nine hour shift and dropping a pitcher of sweet tea or the raw chicken juices from a bag on your foot and totally saturating your sock to be nasty sticky, sickly, soggy, gross, horrible all day long without a change of socks.
Standing: You really need a shoe that fits and is comfortable. If your shoes are too tight you'll never make it through your first double. If they are too loose you may end up spilling something when you trip over your own feet! You will be standing for the entire day. Comfortable shoes are a must. Depending on the size and layout of the restaurant you may be climbing stairs, walking a hundred feet across the building to the kitchen or bar, or you may just be working 12 to 15 hour days without a break. Your feet will thank you. So will your ankles. And back. As well as your knees, legs, hips, etc.
There are dozens of shoe manufacturers that make shoes with slip resistant soles, each one varies slightly and some are better than others. They are also made in varying styles and designs at different price points so they are definitely worth every penny you spend to protect yourself. Most restaurants require slip resistant shoes.
Black is also an industry standard, unless you are Mario Batali, then you do whatever you want. You can get shoes anywhere these days really: WalMart, Payless, online, pretty much anywhere that sells shoes.
My choice: I've worn a form of Birkenstock work clog for the last five years. They are a little more expensive, but worth it in the long run. The clogs are one piece design to provide complete protection from anything in the restaurant, but come with a removable insole used for arch support and formed foot bed comfort. They come up about 2" so I can stand in a puddle and not really have to worry at all about getting my socks wet. No laces, no fuss. Oil resistant. Slip resistant. Chemical resistant. Lightweight. Perfect for me.
When I am going on a formal trip with upper management or working in a fine dining establishment I have a pair of slip resistant wingtip dress shoes from the Shoes For Crews brand. They are extremely slip resistant and fit the bill of a more formal look than my clogs, but they don't compare comfort-wise and I have personally seen employees burn through the SFC brand footware in six month under pretty harsh conditions with the degreaser and various chemicals used in floor cleaning.
I've heard good things about SAS Shoes, but they seem a little heavy for me to have to move around quickly in all day, every week for fifty hours or so.