Switchback is pretty simple, I thought I explained it earlier in this thread, but it might have been a different one. EDIT: I kinda did over on post
#35.
Basically, there are two circuits in the vehicle that go to the turn signal harness. 4 contacts on the bulb and two filaments inside the bulb, one is a low (15W?) draw and one is a high (30W?) draw. When parking lamps are on, the BCM grounds the low circuit, closing it and lighting up the smaller filament for dim amber lights. When the signal is flashing, it repeatedly grounds the other circuit, causing that circuit to close and the larger filament to glow much brighter. As far as I know there is no situation where they are both powered.
Switchback LEDs take advantage of this by having two separate circuits in them with two sets of LEDs. They are the same brightness, usually, because they contain the same number of the same LED chips, just in different colors. The white LEDs are on the same pins in the bulb harness as the smaller filament in the incandescent lamp, and the amber LEDs are on the same pins as the larger filament.
They may do something clever where all LEDs are on the same circuit, but one color is wired in the opposite polarity as the other, and since LEDs only light up when powered in the correct polarity, only one will light up at once, but the operating principle is the same.
This is also how the drop-in brake LEDs work, because your brake/tail lights are wired exactly the same, pretty much. I
think it might power both filaments for brakes, but again the principle is the same. The only difference for the LEDs is one circuit is wired to light up half the LEDs on the bulb, the other lights all of them.