I use transparent and semitransparent watercolor paints and they work very well for my subjects and for layering method. Like most beginners, I too started out with a limited palette trying to mix colors for an exact match. Although it has been a great learning experience, I felt it was time consuming and wasn’t getting clean vibrant results that I was striving for.
So I started to add to my palette a range of shades from warm to cool to grays in each color group that I could use straight from the tube instead of mixing each time over several layers. For e.g. in greens I prefer to have warm greens to cool greens to green grays. So if I need to use a dull green, instead of mixing one, I choose to use green grey straight from the tube (which is a dull green). Similarly, for other groups too like yellows, reds/orange and blues/purples.
I generally find that colors from the tubes are more clean and fresh as opposed to same/similar colors obtained by mixing different hues. This approach gives me quicker and better looking results. Having said that, I still have to mix colors to match variations in the color temperatures, shades and tones.