instead of the HSV implemented in paintstorm,the reason is that when you paint picking the value and then tweaking the hue and chroma
is more convenient than playing with the hsv(the v slider in the hsv stands for brightness of light and not actual value of color) or rgb sliders.
Gimp has the best color sliders in my opinion because it actually visualizes with what value the chroma peaks with each hue,
since the gimp code is free maybe there is a possiblity to port how they implemented their solution to paintstorm.
Also photoshop has lab sliders which offer a simillar workflow of picking value and then tweaking the color.
this is the sliders that gimp has:
this is how it is visualized in the color picker(the chroma peaks at different values)
if would really be cool to have something like this is paintstorm.