I probably have a smaller collection of inks than anyone on this board--only 12 bottles, and three of them are Rohrer and Klingner inks.
Sepia is the only ink I have that isn't in the purple range. I like to use it with my dip pens, for an elegant, vintage look.
Scabiosa is one of my favorite inks, because it shades beautifully, changes color (making it especially suitable for autumn), and looks so different on different papers, but if you want a consistently dark line as opposed to one that shades from dark to light, you will need a relatively wet pen.
Solferino is a very bright ink and hence a favorite of people who consider other Rohrer and Klingner inks too subtle.
In addition, Rohrer and Klingner indicates that one can mix any of their inks, except Sepia. Right now I am using a mix of Solferino and Scabiosa.
Verdigris is a gorgeous, very dark green that I often give as a gift to people whose favorite color is green.