I agree with Lynnie. I also do quite a bit of appliqué using the same method she does. As for appliqueing on the back of a quilt, I think it is fine. I made a quilt for my daughter for Christmas two years ago that was just a scrappy square type of design. Applique did not really fit into the pattern, but I wanted to personalize it, so I appliqued two little ferrets (because they have two ferrets) on the back and they LOVED it. It is really just another way to put your signature on a piece. As for quilting in the design itself, why not? I would just advise you to do that quilting before the sandwich is put together so it does not show up on the front.

There really are no rules to being artistic. Please post a picture when you are finished. ;-)

I would do the applique on the backing fabric before attaching it to your top and batting. You do want to do some kind of stitching around the applique before putting it together or like said by Pickish it will fray.

Good advice from everyone. I'm finding applique to be rather fun!

It sounds like a wonderful idea, using black for the silhouette of the fire truck and/or fireman, probably you might find something in a coloring book. I just found out that my new SIL is a volunteer fireman in the Firemen's Brigade in Sydney, Australia, which I find admirable. My DD was just there recovering from a bad concussion at work, because he wanted to take care of her until her severe migraines started to back off. We've never met him, they did go to the same college with degrees in Aviation Management, but from everything we've heard about him so far, I think we will like him. More importantly, she's happy and that's all that really matters.

You can type "coloring pages fireman" into google...then look at their images...they are free to use
you can put just about any subject after coloring pages, and get tons of ideas.

I think what I am reading about your question can be done. You can highlight anything on the fire truck. It is called an art quilt. I do it all the time.