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That's a tough one. Definitely can't get Photoshop to record in and Action a color selected from the current doc. All color selection tools record the specific color selected at the time the action is recorded.
But in your specific case, here's a method that might work.
1. Select your bone (maybe dupe the layer first cause your are going to destroy it).
2. Expand the selection as desired.
3. Add that selection as a layer mask on your "bone" layer.
4. Click on the "chain link" icon to the left of the layer mask icon in the Layers Pallet. That will record as "Set current layer without layer mask linked"
5. Reselect your bone, then transform it and expand it huge in all directions. Having unlinked the layer mask in step 4, only the color will expand and not the mask.
That will "expand" the current color of the bone across the canvas, but the "expanded" layer mask will restrict it to what you want. Would work on solid color bones. Won't work very well on real bones or objects with varying tone or texture, because the transform/expand will mess up those pixels. But if you transform/expand a solid color you get the same solid color.
From that point you could reselect your layer mask, cut and paste the content on a new layer.