Rainbow

rainbow.js

function rainbow(step) {
var r, g, b;
var h = step / 70;
var i = ~~(h * 6);
var f = h * 6 - i;
var q = 1 - f;
switch (i % 6) {
    case 0:
        r = 1, g = f, b = 0;
        break;
    case 1:
        r = q, g = 1, b = 0;
        break;
    case 2:
        r = 0, g = 1, b = f;
        break;
    case 3:
        r = 0, g = q, b = 1;
        break;
    case 4:
        r = f, g = 0, b = 1;
        break;
    case 5:
        r = 1, g = 0, b = q;
        break;
}
var c = "#" + ("00" + (~~(r * 255)).toString(16)).slice(-2) + ("00" + (~~(g * 255)).toString(16)).slice(-2) + ("00" + (~~(b * 255)).toString(16)).slice(-2);
return (c);
}