My first guess is... the email that you are being sent is being sent
using HTML and you are not seeing the "dark" background to make
the yellow font stand out. However, you say ALL email comes into
you this way. Is all your email from the same place?

I ask because not all people who email use a signature. This would
also seem as if your system is placing a signature on all of your email?

Maybe you could share a little more information. What version of Outlook
do you use? Is it really ALL your email that comes in that way? Do you
use Microsoft Word as your editor?

Nikki