Conditional Format & VLOOKUP (Maybe) on Access 2007 Form Redeux

Preamble:
Please, no comments on the fact that this DB doesn't follow general standards. I can't help that right now. I created previous questions and have attempted to take direction from them of creating relationships and using queries, and none of this worked. A lot of time was put into those responses, so I awarded those experts and now I must move on.  If you can DO THIS FOR ME, great. Otherwise, I'll have to live without it. It must be done in Access 2007 and provided in accdb file format. If necessary, I can be available by phone.

Question:
On the Issue Details form, I would like to conditionally format the "Assigned to" textbox to be fill/back color yellow if the machine's username matches the current user's username in the Contacts list. The dropdown currently contains a combo box with first and last name from a query called Contacts Extended. I did add Username to that query. I just don't know how to proceed.

Thanks so much for your time.
Issues3.accdb