Ok to mimic exactealy what the old painter six watercolor tool does follow my simple instructions.
create a new layer over the canvas.
set the layers blending properties to gel or multiply
paint on that canvas layer with the tinting tool, basic round works good.
and there you have it it works exactealy like the water color tool ,only better cuz you can pick colors with the color picker without drying the canvas, instead of "drying the canvas, just drop the layer.
now start experimenting with the real water color brush in painter & because it the coolest 2-d digital imaging tool I have ever seen.