Regular Flourite is the coarsest material. Black Flourite is a finer grain material, and Black sand Flourite is the finest. Then there is Flourite Dark, which I like, which seems a little finer than regular (red) Flourite. I'm lucky in having a very good LFS here who has most of the Flourites in stock.
I'm using Fluval Stratum now, which is a very dark gray material, with fairly fine particle size, and easy to plant in. And, of course, there is ADA Aquasoil Amazonia, which is also very dark gray-black, very nutrient loaded, but releases ammonia for a month after you set up the tank. And, there are still other commercial substrates.
Flourite is not a source of nutrients for plants. It is high CEC material, so it helps hold nutrient ions from other sources so plant roots can get to them easily. If you want sand, pool filter sand is ideal, because it has the right range of particle sizes, is clean, and has little or no effect on the water parameters. Pool filter sand color depends on where the sand was quarried locally. It is far superior to play sand.