That's how I filled the inevitable gaps in the inlay on my project. Plane a scrap strip close in color to where you need to fill, run a bead of glue over the gap and use a razor blade to push it in, then press as many planer shavings into it as it will take to fill the gap. I used yellow carpenter's glue, and after about 15 minutes I scraped the shavings flush and removed most of the excess glue with a razor, gave it a quick scuff with an old 60 or 80 grit belt (by hand)and wiped with a damp cloth to press any remaining glue and sanding dust into any left over gaps and remove any excess. After this was dry it was very hard to spot, and invisable after sanding.

Tom