Outlook 2007 received message from Outlook 2003 - Hyperlink issues

[Rossco]

Hi,
we have an office that is using a mix of OL 2007 and OL 2003, in exhange
server 2003, and when an email is sent to the 2007 user,and when that user
opens the message the web address at the bottom of the sent email signature
changes from the companies orange colour to a blue hyperlink...

Wheras when sent to another 2003 user, the signature retains its orange
colour....

Any ideas on how to fix/stop this changing to a blue hyperlink?

kind regarsd
Rossco