这是更新的Javascript代码，返回数组中的每个单词，中间的字母为红色。

function iniciar(){
    var texto = document.getElementById("text").value;
    var updatedtexto = texto;
    var palabras = texto.split(/[,]+/);
    console.log(palabras);
    palabras.forEach(function(value,index){
        var wordstr = value;
        var wordLength = value.length; //get length of word
        var centerOfWord = (wordLength/2).toFixed(0); //get centerofword
        var middleLetter = wordstr.substring(parseInt(centerOfWord) - 1,parseInt(centerOfWord)); //get middle letter of word
        var colorWord = wordstr.replace(middleLetter,"<span style='color:red'>"+ middleLetter +"</span>"); //make middle letter color red
        setTimeout(function(){  //remove complete setTimeout if you want show full string with colored letters
            console.log(colorWord);
            document.getElementById("txt").innerHTML= colorWord; //show word
        },550*index);

        //updatedtexto = updatedtexto.replace(wordstr,colorWord);  //uncomment if you want show full string with colored letters
    });

    //document.getElementById("txt").innerHTML= updatedtexto; //uncomment if you want show full string with colored letters
}

希望这对您有用。