How can i do this in a cell formula in excel?

[Phenix]

I want something like this in say cell b1:
=if(now()>a1+14,"RED","WHITE")
where "RED" is the command to change the background color to red, and "WHITE" is the command (or no command at all) to leave it blank.
Range("A1").Interior.Color = RGB(255,0,0)
did not work.
=if(now()>a1+14,Range("A1").Interior.Color = RGB(255,0,0),"")

Basically I put a date in cell a1. If it is 14 or more days later, flag b1's cell red.