Hi,
Yep I'd use NETWORKDAYS and make 4 rules, as TODAY gets included and returns 1 in the NETWORKDAYS formula if you compare two of the same dates, you want to use
=1 (Green)
=2 (Yellow)
=3 (Orange)
> 3 (Red)
E.g.
=NETWORKDAYS($A$1,TODAY())=1 --> Format with a green fill
=NETWORKDAYS($A$1,TODAY())=2 --> Format with a yellow fill
=NETWORKDAYS($A$1,TODAY())=3 --> Format with a orange fill
=NETWORKDAYS($A$1,TODAY())>3 --> Format with a red fill
NOTE: this will leave the cell red if nothing is entered, to bypass this for the red fill CF rule use this formula instead if you don't want to see a red cell:
=AND(NETWORKDAYS($A$1,TODAY())>3,$A$1<>"")