Each opposite pair of pigments on the wheel will produce similar results. If we lean the mixture towards Alizarin or towards Viridian we can get a greyed version of those colours. These mixtures are less intense or dull. To see what colour you have add a dab of white.
You will understand this better by going through the exercise. If not, drop me a line.
A note about adding white; White is the coldest "colour" on your palette. When it is mixed with any pigment it both cools and dulls that pigment as well as altering the value.