Here is a combination of pigments to create a grey. A gradual addition of RMG to Viridian and French Ultramarine. It does not look grey yet, but as more water is added it will be less purple.
Nuance in color is another tool to use in watercolor. A beauty of watercolor is the control of edges. The range of edges from hard and sharp to diffused and almost indeterminate. A hard edge stops the eye. It can create depth. It is a very powerful tool to bring an object out.
Using a flat brush on its tip creates a hard edge. If the paper is still damp the edge will be softer than if it is used on a completely dry area.
Look at the hard edge at the top of the rock. If such an edge was used all over, objects would look cut out. This is true with the flowers as well. Note where hard edges are used where the values are similar. See the dark green splotch in the right corner. It looks splotchy because it is a hard edge all around the object.
Edges are truly fun to play with!