Ebony is the material used for most upright bass fingerboards, though there are many woods that can be used as a substitute. One of the primary reasons is the hardness of the wood so it can resist being worn by the strings. You'll find that pure black ebony has become more rare, and thus more expensive, so you'll find ebony with brown and gray streaks in use on many instruments. My homebuilt EUB has a striped ebony fingerboard that is quite beautiful.

There are stains used for creating more uniform blackness that may have to be reapplied periodically. Aniline dye is one, but I like the black dye that is typically used by leather workers to stain belts, etc. That's not the stuff you'll find in a shoe store, but it is otherwise easily obtainable, search the web for a source.

Relief is the term used for the concave curve that is cut into the fingerboard, to allow the string to vibrate without hitting the fingerboard. If you lay a yardstick lengthwise against the board you'll see daylight in the middle. Unlike bass guitars and similar instruments, the relief has to be planed into an upright bass fingerboard. This is necessary to avoid getting buzzing from undesired string/fingerboard interaction in some positions, and it must be done carefully if you want very low action from your instrument.

You may have seen some bass fingerboards with a sharp rise that runs the entire length of the board, between the A and E string on some basses. It is called the Romberg bevel. That shape is a throwback from when big fat E strings crawled the earth-- the bevel gives more clearance for that string. Some folks prefer it, some don't; it's probably just a matter of what you're used to, but no biggie IMHO.