How do I make black rice turn out better in a rice cooker?
Perfect black rice in a rice cooker - I just cooked 2 cups of black rice, after a single quick rinse using a wire strainer in my Zojirushi rice cooker (fuzzy logic).  I used a standard American measuring cup. I added 3 and 3/4 cups of water (vs. the standard straight 2 waters for every one unit of rice - I do this for ALL rice types as I like a fully intact rice kernel with texture remaining - that fluffs and separates as you expect ).

I also added a crumbled organic vegetarian bullion cube (just one) it adds just a little seasoning (still neutral) but I think also provides a little coating on the finished rice that makes it fluff and separate better.

The rice came out perfectly - tender, with just the right kernel bite, fluffed and separated as expected. 

One other note, I NEVER use the keep warm function and always pop open the cooker at the first bell signaling cooking is complete, unplug, and I fluff immediately - I leave the cooker open a minute or two to allow steam to escape, then I close it. The rice stays perfectly warm after that for a very long time, long enough for a leisurely meal and warm rice for second helpings.

I can't say enough great things about the Zojirushi rice cooker. It is worth every penny. In addition to rice it cooks wheat berry, rye berry, millet , barley, and many other grains ( including perfect oats) automatically ith zero fuss. I have owned two in 22 years and replaced the first only because the bowl was list and the model was discontinued so no replacement bowel was found.

Many blessings in your rice cooking journey!