Well, there are a lot of ways of achieving a similar effect.

The one I explained and used in this mini Fireworks tutorial, is probably the simplest. It’s not ideal, but it gets the job done in a matter of seconds, a few minutes at the most.

You can also use a non-destructive masking technique, outlined very well by Stéphane Bergeron. But it requires a bit more effort, too, and if you’d like to achieve quick, easy results, you would probably use a simple eraser, in some situations… :)

I then use the point-to-point selection tool to rough in a selection, then flood that selection with black to allow the color layer below to show through the mask. I then invert the selection and flood with white to make that area of the mask completely opaque. Finally, I use the airbrush tool to touch up and blend the edges of the unmasked content.

I find it’s much faster this way than just using the erase tool, and if I expose too much, I just add back to the mask to cover it up.