Doable, but annoying.
You might be better off converting HSV to RGB, then just flipping the RGB to GBR.
There are algos for HSV to RGB. @jeff did one here
I mean you could convert to RGB, flip to GBR and reconvert back to HSV, but if you are modifying the pattern and adding logic anyway, just catch the HSV call, convert to RGB, then use RGB(g, b, r) and avoid the 2nd converting back for speed.