Antifreeze schedule

just had my wife take in our taurus 2001 for an antifreeze flush & fill. it's been about 3 years before i realized it "was overdue". i have always
thought that the recommended schedule was two years.
while my wife was having it done i downloaded the owners maintenance schedule and it stated 45,000 miles (car is not a diesel). our mileage was around 46,000 so i felt relieved that i hadn't neglected it.
i thought the antifreeze "breaks down" over time and not mileage hence the old "2 year schedule".
is mileage the new way (i.e. the antifreeze holds up better over time) or what?
also, what is the difference between the various colors (green, orange, yellow). i think ours might be the green but i 'm not totally sure. does the color effect the schedule?
thanks!
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Unfortunately I have a 1999 Ford Taurus with 48,000 Miles, that now has a heating problem because the dealer says that I did not change the antifreeze at 30,000 miles instead of 45,000 like the maintenance schedule states. I will probably have to get a new heater core. I guess that the amount of time is a determining factor on when antifreeze breaks down.
gary wrote:

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