When working on a watercolor painting, it is a good idea to think ahead about what colors you want to use. Choose your colors before you put a brush to paper. If you are planning to paint a large area make sure you create a generous puddle of color or colors.
Here on my palette, I have ready to go primary red magenta, permanent violet bluish and ultramarine blue. I have even mixed a bit of the blue and purple together on my palette. Some colors I like to premix on the palette others I like to make sure I have enough of the color to use but will mix them on my paper.