Paint Curved Surfaces on SketchUp

Question

Working on curved surfaces on SketchUp I would like to use the Paint Bucket in just the part delimited by the plain face not the whole surface as shown below.

Answer

There are several ways to do it. For instance, select the curve you want to replicate.

Then go to Edit > Copy, Edit > Paste, and place it on the End Point

Now you can paint that curved surface closed by that previously pasted curve.