i am using jquery for select drop down value when i select $("#ddlMgArticle option:selected").text(artnam); particular value another value should be same

Its true it will overwrite the selected text but its strange you are assigning value "red" and getting "REd". Provide your current html/Jquery code.

May be you are looking something like this.

$("#ddlMgArticle option").each(function(index){
if($(this).val().length){
if($(this).val().toLowerCase() == artnam.toLowerCase()) {
exists = true; // take index if you want and make it as selected.
}
}
});

if(!exists){
// add it and make as selected
}