Script does not work although the logic is fine

There is a small logic error, and it is that the comparison of coloreado is executed with 0, which is true, but in said result (after entering the if) the variable is set to 1 and therefore it is the next condition is true and the content of the second if is also executed.

An else if solves it, although there are other ways:

var div;
var coloreado = 0;

function clickdiv() {
  div = document.getElementsByClassName("divcolor");
  div[0].addEventListener("click", darcolor, false);
}

function darcolor() {
  if (coloreado == 0) {
    div[0].style.backgroundColor = "red";
    coloreado = 1;
  } else if (coloreado == 1) {
    div[0].style.backgroundColor = "aqua";
    coloreado = 0;
  }

}

window.onload = clickdiv;

.divcolor {
  height: 100px;
  width: 100px;
  background-color: aqua
}

<div class="divcolor">

</div>

Change the second if for an else

if (coloreado == 0) {
        div[0].style.backgroundColor = "red";
        coloreado = 1;
        console.log("Hola soy rojo");
    }
    else {
        div[0].style.backgroundColor = "aqua";
        coloreado = 0;
        console.log("Hola soy aqua");
    }

Greetings is only in the logic of the comparison, at some point it should go through a secondary condition ie an else:

  var div;
var coloreado = 0;;

function clickdiv() {
  div = document.getElementsByClassName("divcolor");
  div[0].addEventListener("click", darcolor, false);
}

function darcolor() {

  if (coloreado == 0) {
    div[0].style.backgroundColor = "red";
    coloreado = 1;
  }
  else{


    div[0].style.backgroundColor = "aqua";
    coloreado = 0;
  }

}

window.onload = clickdiv;

From the technical point of view, it never leaves the first if it is obviously fulfilled but there is never a case of passing to the else