You use the Live Paint Bucket Tool when you have overlapping paths and you want to color, not the paths themselves but the areas formed by the path boundaries.
Live Paint Bucket Tool Icon
When you use the tool, you first select all the overlapping paths and then click once with the tool. That first click causes Ai to:
Place the overlapping paths into a Live Paint Group.
Analyze the path's overlapping areas into distinct regions. Technically Ai looks for edges and faces. An edge is a path that does not intersect any other path. A face is a closed area bounded by edges. So, a face is an area that is undivided by a line segment.
Break the objects overlapping regions into disjoint Face objects and Edge objects. You cannot see these objects in the Layers panel, but on the Artboard, when you hover over a face Ai will highlight its boundaries with a thick line, and when you hover over an edge, Ai will highlight the face's edges with a thin line.
Faces and Edges
Now you can color Face Object's fills or strokes by changing the current color, and then, on the artboard, clicking on the faces or edges to which you want to apply the color.
Keep in mind that, while you can apply fills and strokes to Face Objects, they are not real paths, and you cannot change their opacity, apply effects, or do many of the other things that you might expect to be able to do to paths.
Using Live Paint
Live Paint - Before and After
To use the Live Paint Bucket tool (k) in Adobe Illustrator:
Double click the tool to display its Options panel and check the checkboxes to tell the tool if you want to color faces (fills), edges (strokes), or both. Assume for what follows that both are selected.
Select the set of overlapping paths that you want to paint.
In the Swatches panel, click in a Swatch Group that you want to use to color the figure that you want to paint.
Get the Live Paint Bucket (shortcut: k-key) and click once with the tool on the selected paths. Ai will place the paths into a Live Paint Group and will create Face Objects and Edge Objects that represent the areas where the paths overlapped.You cannot see Face Objects and Edge Objects in the Layers panel, but you can see them on the Artboard when you hover over them with the Live Paint Bucket tool. When you hover over a face, Ai will highlight its boundary with a thick line. When you hover over an edge, Ai will highlight the edge with a thin line.
Paths During the Live Paint Process
Color the faces and edges that you want to color by repeatedly doing the following:
Go to the Appearance Panel and select a fill and a stroke color.
With the tool, hover over a face or an edge. When you see the thick face highlight, or the thin edge highlight, click the tool. Ai will apply the fill or stroke color that you set in the Appearance panel.
