That's clearly a Norway Maple (Acer platanoides) Leaves of Norway Maple are broader than those of Sugar Maple and have 5-lobed leaves. Sugar maple also has 5 lobes but the 2 base lobes are much smaller than Norway Maple. There should be milky sap in petiole and leaf veins if it's a Norway Maple (probably none or not as much milky sap in dry fall leaves than green leaves).

The green pigment is chlorophyll. It's there, or your tree wouldn't be. ;o) The leaves contain chlorophyll and are carrying on photosynthesis or the lack of auxin flow across the abscission layer would cause leaves to drop. It could be a mutation, but more likely not. I would look to injury, and my guess would be damage to water transport system, maybe something like canker clogging vascular system causing accellerated senescence (aging) of leaves. Others more expert than I may have other ideas. Al

Plenty of ways to kill a tree...the problem is that you'll have a very large (I assume) dead tree to deal with after the deed is done, and large dead trees are inherently dangerous. It costs a bunch of money to pay a professional to cut down a large tree because it's hard work with serious risks attached. If you want the tree gone and it's too big to do it safely yourself, you really should pay a pro to do it. If you like, call another arborist and get another estimate. Dave

It looks like some varieties of red maple might work well. There appear to be varieties that are perfectly happy in florida, which have no chill requirements to break dormancy. Sugar maples, however probably wouldn't do particularly well. One article I found states that they require 2500 continuous hours of chill (below 41f) to break dormancy. Without that chill, they'd probably do well enough for a couple years, but eventually would either go dormant and not come out of it, or they'd just die from the stress of not being able to rest. Here is a link that might be useful: Top of page 3 references the lack of chill requirement for floridian acer rubrum