Amazing things happen when two pigments are allowed to mingle and flow into each other. I term this "floating" colors. Really it is a wet-on-wet application of paint where two pigments are mixed while the paint is still wet.
This method takes a very delicate light touch and should not be overworked (brushed again-and-again) or the effect will be lost. For the above photograph I used Ultramarine deep and mixed it with water to get a coffee like consistency of paint. I did one brush stroke of the of this blue color. Then I allowed the pigment to slightly settle into the paper for a minute or two. Note: This pigment is a coursley ground granulating pigment. While the pigment was still wet I used a Quinacridone violet with a little less water than the blue (if you use more water there will be a watercolor bloom). I gently brushed this color into the wet ultramarine allowing the brush to just touch the paper and trying not to diturb the blue underneath. An interesting thing happens in that the finely ground pigement moves the granulating pigment. Again I stress this is only 2-3 brush strokes and I do not go over it or I disturb the paint and the way they "float" one on top of the other would be ruined. I just love the way watercolors mingle in this manner and every 2 pigments "float" a little differently depending on which is laid down first, along with the density and mixture of water. This is what makes a watercolor painting interesting! Give it a shot try floating your watercolor pigments and let me know how it works.