来自php页面的电子邮件中缺少颜色

I am sending an HTML email from my website form via php, and some of the category words are in blue, but one of them (the word "Airport:") is in black, despite the code showing it should be in blue. My code:

$message = '<html><body>';
$message .= '<span style="color:#000fff;">Username: </span>'. clean_string($user) . '<br />';
$message .= '<span style="color:#000fff;">Code: </span>'. clean_string($code) . '<br />';
$message .= '<span style="color:#000fff;">Old Phone Number: </span>'. clean_string($oldphone) . '<hr />';
$message .= '<span style="color:#000fff;">Contact: </span>'. clean_string($contact) . '<br />';
$message .= '<span style="color:#000fff;">Email: </span>'. clean_string($email) . '<br />';
$message .= '<span style="color:#000fff;">Telephone: </span>'. clean_string($telephone ) .'<br /><br />';
$message .= '<span style="color:#000fff;">Business name: </span>'. clean_string($name) . '<br /><br />';
$message .= '<span style="color:#000fff;">Address line 1: </span>'. clean_string($address1) . '<br />';
if(!empty($address2)){
$message .= '<span style="color:#000fff;">Address line 2: </span>'. clean_string($address2) . '<br />';
}
$message .= '<span style="color:#000fff;">City/Town: </span>'. clean_string($town) . '<br />';
$message .= '<span style="color:#000fff;">County/State/Province: </span>'. clean_string($county) . '<br />';
$message .= '<span style="color:#000fff;">Postcode/Zip: </span>'. clean_string($postcode) . '<hr />';
$message .= '<span style="color:#000fff;">Accom Type: </span>'. clean_string($accom) . '<br />';
$message .= '<span style="color:#000fff;">Rates From (&pound;/$/&euro;)  </span>' . clean_string($rates) . ' - per ' . clean_string($period) . '<br />';
$message .= '<span style="color:#000fff;">Airport: </span>'. clean_string($airport) . '<br />';
$message .= '<span style="color:#000fff;">Distance: </span>'. clean_string($distance) . '<br />';
$message .= '<span style="color:#000fff;">Website: </span>'. clean_string($url) . '<br />';
$message .= '<span style="color:#000fff;">Picture: </span>'. clean_string($thumb) . '<br />';
$message .= '<span style="color:#000fff;">Intro: </span>'. clean_string($intro) . '<br />';
$message .= '<span style="color:#000fff;">ETC: </span>'. clean_string($ETC) . '<br />';
$message .= '</body></html>';

The word "Airport:" is clearly inside the tag that should make it blue but in the email it is black. All the other words inside identical tags correctly display in blue. I can live with it being in black, but I am totally stumped as to why the blue tag does not work for just one word.