I've just received an email update from the National Theatre, advertising The Hour We Knew Nothing of Each Other. Underneath a large image advertising the show was the following text:

Intrigued by this obscure message I wanted to know more, so I clicked and dragged my mouse to highlight the surrounding text. Having exposed it, I clicked the link to view the email if you can't see the graphics (sadly there wasn't one to click if you couldn't see the text).

-------- We have sent you this email as you opted-in to receive information from the National Theatre when you registered online, booked tickets or took out a membership with us. To change your contact details, or to add/remove yourself from a list or to unsubscribe from this list (or all our lists you are subscribed to) login at this link and update your details. If you can't login and you want to remove your details from our lists, reply to this email with unsubscribe in the subject line. To forward this e-mail to a friend or colleague, visit this link -------- Registered name: The Royal National Theatre Company no: 749504 registered in England Charity no: 224223 Registered office: Upper Ground, London SE1 9Px

 

 As I suspected, the text was white on a black background, and the background was set to black using a style in the HTML header.

There are two lessons to be learned from this example, firstly always test your email in several email clients, not just the one you use, before you broadcast it.

Secondly, don't use styles in the HTML header as several clients, particularly web based ones (in this case Yahoo) will ignore the style.