How to display a value from a radio button in the options menu in wordpress

Your form is sending data using POST method, so you should receive selected value of radio button in $_POST['colorSelect'].

To simply display it you can use:

if(isset($_POST['colorSelect']))
    echo $_POST['colorSelect']; 
else echo "Nothing selected";

To save it to options table use following code at the start of your function colorSelector():

if(isset($_POST['colorSelect']))
    update_option('colorSelect', $_POST['colorSelect']);

So you can always retrieve it later using get_option('colorSelect');

I hope this will help.

It is advised for best practice that you should follow WordPress Setting API, if you have more options to save.