https://extensions.sketchup.com/extension/66564e2c-9c36-4006-aafc-7da918665e95/eneroth-layer-painter
Swiftly apply layers to entities in a Paint Tool-like fashion. This allows for quicker application of layer to entities without having to look up the layers by name each time.
Activated from Extensions > Eneroth Layer Painted or the toolbar.
Personally I use Alt+L as shortcut for this extensions (I use L for Line Tool, and Ctrl+L, Shift+L and Ctrl+Shift+L for Eneroth Swift Layer Visibility Controls).
If the model is saved and SketchUp closed while the tool is active the Color By Layer display will be enabled when the model is next opened. To disable it, click the Details arrow in the Layer panel and untick Color By Layer.
Due to limitations in the API layers cannot be picked from entities outside of the active drawing context the way that would otherwise be consistent with native paint Bucket Tool.