Ink is pretty much the same dye and water; some have more colors (variety), some will be more saturated (darker) than others. All-in-all try several brands/colors and see what you like.
Above all DO NOT use calligraphy or india ink. These contain binders (usually shellac) & usually pigments (as opposed to dyes, even if they say fountain pen safe) and will gunk up your pen permanently.
Above all DO NOT use calligraphy or india ink. These contain binders (usually shellac) & usually pigments (as opposed to dyes, even if they say fountain pen safe) and will gunk up your pen permanently.