Twilight is a third party app. It draws a red layer on top of everything else. This is why the system displays a notification : it wants you to know that an ap

Twilight is a third party app. It draws a red layer on top of everything else. This is why the system displays a notification : it wants you to know that an app is drawing on top of everything. The system settings works very differently, it directly applies a matrix to what needs to be displayed. This is way more efficiencient since applying this matrix is basically free instead of adding one layer with alpha composition. It also allows other customizations, like adapting the screen for deuteranomaly. Ideally, Google should open the API behind this feature at some point.