You can have as many formulas/statements that you want in conditional formatting but FMP executes ONLY the last encountered "true"
you need 2 formulas:
1) status = "Unpaid" and date < get ( CurrentDate )
Fill color => red
2) status = "Paid"
Fill color => black
As coherentkris said, if two conditions affect the same properties (fill color in this case) and both conditions are true, the last one will be taken into account.
You really have to make sure that your conditions are as specific as possible to avoid the possibility of 2 of them being true at the same time (only if they affect the same properties, else you don't care)
Thank you both very much it has helped me a lot.
One thing though you refered me to another post which has conditional formating fp7 in a zip and I cant open that on my mac as I am using fp12 and izip, is it possible to change it to fp12 or copy and past it on here so I can see it.
OK Guys I have worked it out thanks for your input I even managed to set the field to bold when red.