Spade bits are usually produced uncoated. The benefits to a spade bit’s performance that can be provided by coatings are negligible, and adding a coating to a drill bit raises its price.
Coatings can provide corrosion resistance in storage, which has led to their application by some manufacturers.
Titanium nitride is a hard, gold-coloured coating that will protect your bit from wearing down. Once you sharpen the cutting edges, though, the coating will be worn away.
This kind of coating is much more useful on bits that are designed to cut metal and other similarly hard materials.
Black oxide is much less hard wearing than titanium nitride. It is an iron-based coating that provides limited corrosion resistance. While it doesn’t perform as well as titanium nitride, it is cheaper, meaning you can acquire tools that have a degree of rust resistance without going on a spending spree.