Hi. There's too many problems in your code...so I rewrite your code...
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>Test</title>
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</head>
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<script language="javascript">
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<!--
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function validateForm(Qform)
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{
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var incorrect = new Array();
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var no = 0;
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for (var a = 0; a < Qform.elements.length; a++)
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{
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var field = Qform.elements[a];
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if (field.value.length <= 0)
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{
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incorrect.push( field );
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no ++;
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}
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else
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{
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field.style.backgroundColor="";
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}
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}
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for( j=0; j<no; j++)
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{
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incorrect[j].style.backgroundColor="#FF0000";
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}
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if ( no > 0)
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{
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incorrect[0].focus();
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return false;
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}
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else
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{
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return true;
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}
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}
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-->
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</script>
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<body>
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<form action="" method="post" onSubmit="return validateForm( this );">
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<span id="1">Title: </span>
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<input name="id" id="title" type="text" size="25" maxlength="6">
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<br />
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<span id="1">Content: </span><input name="content" id="content" type="text" size="25" maxlength="6">
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<br />
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<input id="submit" type="submit" value="OK" />
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</form>
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</body>
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</html>
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I use incorrect array to save invalid field object,not index as you did. and pay attention to
onSubmit="return validateForm( this );
you should pass a form object into validateForm,and the function must return a bool value, return false means the form will NOT be submit. if you didn't return a value,the form will be submit everytime.
hope it helps.
[Javascript] Change color in the field 
