Anyone ever seen a really dark olive duck egg?

[PrairieFarmer]

Hi! I have now found two really dark olive green duck eggs. So dark, that both times I thought the egg was literally covered in mud (both times I found the egg in my "outer" pen which can get pretty muddy this time of year). But now, it is really a super dark olive green. I've never seen a duck egg that dark before. Anybody else? Or any ideas which duck is laying it?
I have Khaki Campbells, Blue Swedes, Rouens, Chocolate Runner and then some "combos" of all those.

 

[duckyfromoz]

I have seen them from Black Runner ducks and Cayugas in different shades of green to black. I am told that when an occasion very dark shelled egg is laid- the eggs spends more time in the part of the reproductive tract where the shell is formed- sometimes these darker shelled eggs have an especially thick shell. I dont keep either - but have some that do lay a green tinted egg- and the depth of colour can vary slightly- but as to which of your ducks the egg came from... ?? IDK since they too would usually only lay white or green eggs. Making you could try putting colouring on the vent of some of them to work out who. Food colouring or lipstick on the vent- in different colours - and then match the egg with traces of colour to the duck.

 

[PrairieFarmer]

Well that's interesting! My duck eggs have typically run in color from off-white to a light blue-green. I have one 3 year old chocolate runner hen and then I have a young (this would be her first laying season) hen that appears to be a combo between chocolate runner and probably blue swede. She's more upright but also more bulky. Wonder if a dark egg like that would be more likely to come from an older hen or a just starting to lay one? I've only seen 2 eggs like that spread out over about 2 weeks. If I keep seeing them I'll try the vent thing.