Generally, in the black market, there are three types of heroin. Their differences lie in color and the refinement process.
The first and most common is
brown sugar, with a brown appearance and more basic characteristics. It's usually the most common.
The second is
white heroin, which is generally associated with higher purity.
The third is
black heroin. Generally, this type doesn't have a clear purity and can vary widely. It's stickier and tar-like.
Bonus: Pharmaceutical heroin. It's the purest, either liquid or powder form, and generally colorless. My profile picture is an example of this type of heroin. Bayer was the first pharmaceutical company to isolate and produce heroin from morphine. The process generally involved adding an acyl group to morphine and then neutralizing it with an alkaline solution.
"Bayer" or chemically pure heroin is the best of all. It's probably a thousand times better than any crap that typical junkies have tried and likely the closest thing to heaven anyone could experience.
Today, it's practically impossible to find, and I've seen that it's only used in Switzerland as a treatment for severe pains, such as those typically associated with cancer, and I believe also for addicts.
Postscript: I'm not a junkie and have never tried heroin, and honestly, I don't think it's advisable to do so. Think about it, trying something that reduces all other aspects of your life to trivialities or nothing at all will enslave you to it.
Another postscript: I'm not an expert, I'm just providing general references.