All but the very early 5000s are all red. About the biggest difference that I know about is that most 5660s have 3 amp charging systems and most 5665 have 15 amp systems. My 5665 has an hour meter and my 5660 does not. It all kind of depends on the year it was made.
Other than that, they are pretty much the same, awesome machines.
Other than that, they are pretty much the same, awesome machines.