Sorry no pics at the moment. But I will tell you eggsactly what I did!
Not lipstick, but the little bottles of cheap liquid food coloring. Because I've been working around in my kitchen, I happened to find blue & yellow tubes that I used. Of course, 2 colors meant I could only test 2 ladies. I did consider mixing to get a 3rd, but to be honest, the experience kind of freaked out the flock, so I just left well enough alone at 2.
Ok, so what I did was gently pick up the duck and sort of get myself into a seated/crouched position on milk crate. Then I flipped the duck over so her underbelly was exposed and I talked quietly to her and she actually was quite calm. Then I sort of tucked her head under my armpit, like a football. Then I located the vent, gently opening a tiny bit, and squirted a little coloring in. Then the next day I found the egg, streaked with blue. Now that duck was white, so she walked around with a blue bum for 2 days, but today after her bathing, the blue is pretty much gone. And the eggs I've collected yesterday & today have been pure white.
Now about the yellow: I didn't see a yellow egg. So either the yellow just wasn't as visible as the blue was and I missed it, or the duck that I gave the yellow drops to is the one with the issue. So now that time has passed, I will treat that duck again with the blue, since I know it works, and re- evaluate.
About the lipstick, I know from my own experience it seems like there are 2 kinds of lipstick: the kind that wears off really quickly and the stuff that is long wearing that is really waxy. I don't feel right about putting the waxy stuff there. And the glossy wear off stuff seems like it wouldn't last long enough to work, but I don't know, didn't try it.