Fill, adjustment, Remove and Clone layers · Layer Comp

Fill layers

Solid colour, or a linear or radial gradient between two colours, each with its own alpha. Radial starts as a vignette, linear as a sky fading down.

Edit Gradient drags the start and end points on the image.
Pick Color from Image (I) picks a fill colour; Ctrl-click sets a gradient's end colour.

Adjustment layers

Curves, Hue/Saturation, Color Balance, Exposure, Brightness/Contrast, or Empty. They apply compositor nodes to everything below, limited by their mask and opacity. Clip one to a layer to adjust only that layer.

Remove (Shift+Backspace)

Turns the selection into a Remove layer: a hole cut into everything below, filled by the Inpaint node. It's live, so changes underneath flow through. Make the selection a little larger than the object; the fill comes from the hole's edge.

Clone Stamp (Shift+S)

Alt-click a source, then paint. Each source makes a Clone layer whose mask you paint in.

Along Surface (the toggle beside Clone, on by default): when the source is on scene geometry, the copy follows that floor or wall in perspective, like Photoshop's Vanishing Point but from the real scene. Tiles cloned toward the camera grow; cloned along a wall, they slant with it.