Sorry for the delayed response. Here it is.
So here is the initial problem at first blush, the color itself has 8 "alternate mixes" to the paint product, meaning their are 8 variations of the same color code, sprayed at different times on the assembly line. Second, you are down to the raw base material of the bumper material, you now need to add a primer, then sealer, before you use the touch up paint. So, what you need to do now is as follows:
1: You need a micro sanding wand, the head, about the size of a "Q" tip, carefully sand down the bare area, and the very edges of the area where paint is still attached.
2: Wipe down with an automotive grade de-waxer/degreaser
3: Once dry, I suggest you use a foam "Q" tip (buy a small box) to apply a primer, or primer/seal combination, light, even strokes, and several layers until you do not see the black bumper material.
4: Next is the application of your color, again, light, even strokes, and very light coverage layers until the primer is completely covered.
5: Once accomplished, you can then do the same with a clear/top coat. Again, clean, even, light strokes and coverage.
Allow each layer to properly dry/out gas before adding another on top.
6: Walk away for an evening, come back the next day and see if it needs a light hand buffing
What I recommend, go to your local autobody shop and let them prep and blend the paint within the bumper itself. Do it once, do ir right, and forget about worrying about it or getting yourself wound up about it every time you see the homemade repair job.
Bill S.