!preg_match for letters not working

I am developing a website in which I use !preg_match("~/^[a-zA-Z ]*$/~",$name) that when user write his/her NAME in the HTML FORM field only LETTERS allow to write if number write message appears "Only letter allowed".... But it takes both Numbers and Letter. what to do??? here is my code:

<?php
    $nErr = $naErr = $cErr =  "";
    $id = $name = $color =  "";

    if (isset($_POST["submit"])) {

         $id = $_POST["id"];
         $name = $_POST["name"];
          $color = $_POST["color"];

        if (!preg_match("[0-9]",$id)) 
         {
           $nErr = "Only number allowed"; 
         }
           else if (!preg_match("~/^[a-zA-Z ]*$/~",$name)) 
         {
           $naErr = "Only letters allowed"; 
         } 

         else if (!preg_match("~/^[a-zA-Z ]*$/~",$color)) 
        {
           $cErr = "Only letters allowed"; 
         } 
       }
    ?>