JSFiddle - React, Tailwind, and code Playground

HTML

<div id='colors'></div>

JavaScript

function RainBowColor(length, maxLength)
{
    var i = (length * 255 / maxLength);
    var r = Math.round(Math.sin(0.024 * i + 0) * 127 + 128);
    var g = Math.round(Math.sin(0.024 * i + 2) * 127 + 128);
    var b = Math.round(Math.sin(0.024 * i + 4) * 127 + 128);
    return 'rgb(' + r + ',' + g + ',' + b + ')';
}

for (var i = 0; i <= 255; i++) {
    $('<span>&#9608;</span>').css({
        color: RainBowColor(i, 255)
    }).appendTo('#colors');
}