[рони]

ВэйДлин,
да и ваш код вполне рабочий с поправкой

function RGBtoHSB(RGB_r, RGB_g, RGB_b){
	var Min, Max, D, H;
	Max = (RGB_r > RGB_g) ? ((RGB_r > RGB_b) ? RGB_r : RGB_b) : ((RGB_g > RGB_b) ? RGB_g : RGB_b);
	Min = (RGB_r < RGB_g) ? ((RGB_r < RGB_b) ? RGB_r : RGB_b) : ((RGB_g < RGB_b) ? RGB_g : RGB_b);
	if(Min == Max) {
		HSB_h = 0;
		HSB_s = 0;
		HSB_b = Max / 255;
	} else {
		if(RGB_r == Min) {
			D = RGB_g - RGB_b;
			H = 3;
		} else {
			if(RGB_g == Min) {
				D = RGB_b - RGB_r;
				H = 5;
			} else {
				D = RGB_r - RGB_g;
				H = 1;
			}
		}
		HSB_h = (H - (D / (Max - Min))) / 6;
		HSB_s = (Max - Min) / Max;
		HSB_b = Max / 255;
	}
	HSB_h = HSB_h * 360;
	if(HSB_h == 360) {
		HSB_h = 0;
	}
	//HSB_h *= 100;
	HSB_s *= 100;
	HSB_b *= 100;
  alert(Math.round(HSB_h) + ' - ' + Math.round(HSB_s) + ' - ' +Math.round( HSB_b));
}
RGBtoHSB(127, 212, 255);