Spot Remover?
 

My latest quilt has a white background and has acquired various dirty spots in the construction.

Does anyone know of an effective spot remover that won't harm the fabric?

After the quilt is finished, wash in warm water with a couple of color catchers. If the spots are still there pre treat with most any stain remover and wash again. Don't put quilt in dryer until spots are gone. I found trying to spot clean usually spreads the cleaning and leaves a water mark.

I would get the quilt finished and then you can wash it.

What about a mark from my dirty iron? I was thinking about spraying it with a prewash.