Can you tell which duck these eggs belong to?

[soccrkep1]

I have a white layer, Welsh, and 2 Buffs, all barely over 5 moths. They live together and it's not worth their stress for me to separate them to find out who's laying, but I was wondering if there is a way to tell their eggs apart by color or size, or something? It's not a big deal, I'm just curious. I got 2 eggs the first day, and 1 egg every day since for the past week. It's pretty cool because this is the coldest weather we've seen this year and someone's laying!

 

[Amiga]

Our Buffs lay cream-colored eggs. I think I recall someone dabbing a little food coloring on a duck's vent to see if she was laying.

 

[Sfraker]

My WH lay white eggs.

Put a dot of food coloring in some vaseline and dab it on the ducks vent before bed. You can then match the colors to know who is doing what.