What the difference between gem based, dust based, and ingot based?

It just allocates what type of texture the item/material will use. Gem-based will select a random type of gem in your selected colour, that may look like a diamond, lapis lazuli or something entirely new. Ingot-based makes it look like an ingot, although it doesn't add a raw material. Powder-based will look like gunpowder or redstone dust. It also changes the name after your material name, eg. {material type} - gem, {material type} ingot - ingot, {material type} dust or powder (I forgot which) - dust.

Hope that helps!