If you really want to know which ones are laying which egg, try putting some food coloring in the vent each morning. I would not use red since they like to pick at red, but if you put a different color in three of them each day, you should know within a few days which are laying. I'd certainly think the darker one is probably a Welsummer egg but no guarantees.
They would still rearrange, and I would sometimes end up w/a bare spot...just where they would lay and sometimes "dent" or crack an egg in the process. I solved that by lining the bottom of the box w/corrugated cardboard for some cushioning effect. Just replace when dirty
) Sometimes all boxes will be used, sometimes 4 eggs in one and the others empty...go figure!
