Why is my fluorescent tube orange on one side, white on the other and dark in the middle?
Your fluorescent tube has filaments on both ends. Those filaments are heated by the starter current and then emit electrons into the gas filling of the tube. To assist that, they have a coating of lanthanides.

Over time, those lanthanides amalgamate with the mercury gas filling and cannot serve their function any more. The tube cannot be started any more then. It will be heated up through the filaments until the starter opens, but as nothing happens then, the starting process is repeated.

What's still there is the filaments. Depending on the amount of lanthanides still in function, electrons are still emitted and excite the mercury gas filling in the surroundings of the electrode. That's the green or white end. At the orange end, what you see is the glowing of the filament.