The process you are describing is often called ebonization. There are a few issues you will run into.
1. Its hard to get a REALLY jet black color in wood. Thats just the nature of most dyes and the way wood ages.
2. Jatoba is a terrible choice for an ebony substitute. The defining feature of ebony is not just its color, but its incredibly fine grain that produces a smooth, satinlike surface. Jatoba is a very coarse grained wood. Traditional ebony substitures are woods like Holly and Boxwood, both of which not only have a very fine grain, but are very pale white and consistent and color to facilitate the dying process.
Whata re you looking to do with it? Do you want to make a knife?
Ask yourself this. Does it NEED to be jet black? If not, African blackwood is an amazing substitute, its harder, stable, fine grained and very dark. If it must be jet black, use black paper micarta.
