How to tell who's laying what?

[TigerLilly]

Is it safe to assume/hypothisize by reason of deduction that a new, smaller & darker brown egg was laid by a 1st timer? If so, I think I know which one has started laying, but of course since I wasnt there I can only guess...
I have 2 buff orpingtons--one of them is about 1 yr & I know she's laying. The other is about 6 mos. old, but her comb is not RED like I hear people talking about, so I'm thinking it's not her.
I have 2 barred rocks--one is about 20-22 wks with a comb that's really red like the B.O. that's laying; the other one is about 19-20 wks with a comb like the younger B.O.
Would I be correct in thinking that the B.R. that is older should be the one laying?
Did any of that make sense or was it too confusing?

 

[TigerLilly]

Here is a pic of the newest one I think is laying:

I know Ethel is laying:

And here are the other 2 that I don't think are laying yet:
Thelma:

Lucy:

 

[CityGirlintheCountry]

If you are really desperate to figure out who is laying what, you can coat their vent with food coloring. The eggs will be streaked with that color. Otherwise, you have to catch them in the act.

 

[TigerLilly]

Well, I guess I'll be hanging out in the coop tomorrow! That'll be easier than the food coloring...