Adjustment Layers

An adjustment layer applies its effects to everything beneath it in the layer stack — no content of its own, just a pass-through that transforms whatever’s below. Stack a color-correction or blur effect on it and every layer underneath gets that treatment, without duplicating the effect onto each.

Create one with ⌘⌥Y or from the Layer menu, or right-click (New > Adjustment Layer) an empty area in the Viewport or Timeline.