A derby shoe is quite similar to an oxford, with different lacing. A derby has an open lacing. The two tabs at the top of the tongue (on each side) are not stitched together at the bottom. Pay attention to the photo below. Compared to the oxford, without lacing, the tabs will not still stick together because the two tabs are separated.
In the USA Derbies are sometimes referred to as Bluchers.
Because the difference between an oxford and a derby isn’t that much, it’s hard for most people to recognize it. Subsequently, between an oxford and a derby, it’s simply about personal preference. If you have to own one of those, know that oxfords are much dressier, and don’t play well with your casual wardrobe. Whereas derbies are slightly more versatile and forgiving than oxfords.
If this is your first pair of oxfords, choose black. But it will require another investment into a brown loafer. If you can’t afford a brown loafer in the near future, go for a dark brown oxford. The reason is that a black oxford can work with your navy and charcoal suit. You can also get away with it as formal wear if it’s spotless and freshly shined. But it won’t help you in the ‘blue jeans Saturday’ appearance, so you’d need that brown loafer. And, for the sake of the shoe, don’t wear it everyday.