Changing Field Style for Problem Tasks if due date is passed

I'm trying to change the font color of the due dates in the list view of PTASKS if the due date is past, but no matter what I try it doesn't seem to work.

Here's what I have now:

Table: Problem Task [problem_task]

Field Name: Due date

Value: javascript:gs.dateDiff(current.due_date.getDisplayValue(),gs.nowDateTime(),true) <  0 ;

Style:  color:red;

What am I doing wrong?

Also, where can if find a comprehensive list of styles  (colors, background, font sizes, etc.) ?