Looking at the difference in atmosphere created by the use of one additional colour:
Paper: Bockingford 190gsm CP (NOT)
Winsor Violet, Neutral Tint and Burnt Umber painted wet in wet for an atmospheric, watery, misty landscape.
Winsor Violet, Neutral Tint and Burnt Umber painted wet in wet. The addition of dilute Pthalo Turquoise gives the image a much lighter and more watery feel.