I have been stumped on this for a while. I'm trying to add a hidden closure to a seam on a garment that has already been sewn. I thought about using a zipper, snaps, and velcro.

I tried sewing in velcro into the seam allowance but I can see the edges of the velcro when it when its fastened because the velcro is black. If I could dye or paint it to be a close match to the fabric, it might work, but I don't think it would take any dye (at least not the hook side) and I think any kind of paint would render the velcro inoperable, unless there is some kind of special paint that would do the job without messing up the hooks and loops.

I tried putting snaps in the seam allowance but snaps leave a small gap (maybe 1/8") so you can see them when looking at them on edge.

Zippers I don't know about... I think I would have to put the zipper in before the seam is sewn, at least if I want it hidden. That is what the instructions I have read all indicate.

Any ideas? Is there something else I'm not thinking of?