retrieve choice value with jsom

I'm trying to retieve a choice value that a suer has selected from a dropdown list with :

var oTextColour=oListItem.get_item('myChoice');

But I get null when alerting the value.

I've tried :

var oTextColour=oListItem.get_item('myChoice').get_lookupValue(); but this errors.

Any ideas, using javascript

More Code

function retrieveListItemsAU() {

   var clientContext = new SP.ClientContext();  
   var oList = clientContext.get_web().get_lists().getByTitle("AboutUs");  
   var camlQuery = new SP.CamlQuery();


camlQuery.set_viewXml("<View><Query><Where><Eq><FieldRef Name='_ModerationStatus'/><Value Type='ModStat'>0</Value></Eq></Where></Query></View>"); 
this.collListItemAU = oList.getItems(camlQuery);
clientContext.load(collListItemAU);
clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceededAU), Function.createDelegate(this, this.onQueryFailedAU));        

}


function onQuerySucceededAU(sender, args) {

        var listItemInfo = '';
        var table = '';
        var image='';
        var lookupVal='';

        var listItemEnumerator = collListItemAU.getEnumerator();

while (listItemEnumerator.moveNext()) {

    var oListItem = listItemEnumerator.get_current();
    var oTitle=oListItem.get_item('Title');
    var oDescIntro=oListItem.get_item('Introduction');

    //var oTextColour=oListItem.get_item('myChoice');
//alert (oTextColour);


} // end while loop

} // end function