JSFiddle - React, Tailwind, and code Playground

JavaScript

var div = document.createElement('div'),
    first = 'First JavaScript string.',
    second = 'This is second text.',
    combine = first + ' ' + second,
    colored = '';

div.id = 'sort-text';
document.getElementsByTagName('body')[0].appendChild(div);

var curr = -1;
var ignore = ". "; // Ignore space and period
colored = combine.split("").map(function(x) {
    if (ignore.indexOf(x) >= 0) return x;
    curr++;
    if (curr % 2 === 1)
      return '<span style="color: #d10;">' + x + '</span>';
    return x;
}).join("");

console.log(colored);

div.innerHTML = colored;