function rgb2hsv () {
    var rr,gg,bb,r = arguments[0] / 255,g = arguments[1] / 255,b = arguments[2] / 255,h,s,v = Math.max(r,g,b),diff = v - Math.min(r,diffc = function(c){
            return (v - c) / 6 / diff + 1 / 2;
        };

    if (diff == 0) {
        h = s = 0;
    } else {
        s = diff / v;
        rr = diffc(r);
        gg = diffc(g);
        bb = diffc(b);

        if (r === v) {
            h = bb - gg;
        }else if (g === v) {
            h = (1 / 3) + rr - bb;
        }else if (b === v) {
            h = (2 / 3) + gg - rr;
        }
        if (h < 0) {
            h += 1;
        }else if (h > 1) {
            h -= 1;
        }
    }
    return {
        h: Math.round(h * 360),s: Math.round(s * 100),v: Math.round(v * 100)
    };
}

和如何使用它：

console.log( rgb2hsv(60,120,180) );