One thing you need to realize is that the depth of colour of an egg varies over the laying cycle. This occurs with both blue and brown (and presumably olive) eggs. Obviously not with white. Anways, as the laying cycle begins, the egg is about as dark as it will ever get (for a first time layer, that may not be entirely accurate, as the bird is just starting to exercise all the "stuff" that goes into making eggs). Gradually, as the laying cycle goes on, the pigment will deplete and the eggs will get lighter in colour. The the bird will go broody and raise a clutch, or molt, and spend a few weeks no laying. Once she starts up again, her eggs will again be dark.
Now, as others have said, HOW dark varies, as does the actual HUE. To me, even the "bluest" of eggs still has a bit of green look to it...to me a true blue is much closer to lavender/purple on a colour chart than the colours we see in blue eggs (including robin's eggs).
I have seen egg colour charts that link depth of colour with a number. Perhaps google? Anyways, my guess would be that the HUE would be at least as important to you as the depth of colour, but then I am not you. Personally the olive-coloured eggs are something I do not find at all attractive. But obviously many people do.
Now, as others have said, HOW dark varies, as does the actual HUE. To me, even the "bluest" of eggs still has a bit of green look to it...to me a true blue is much closer to lavender/purple on a colour chart than the colours we see in blue eggs (including robin's eggs).
I have seen egg colour charts that link depth of colour with a number. Perhaps google? Anyways, my guess would be that the HUE would be at least as important to you as the depth of colour, but then I am not you. Personally the olive-coloured eggs are something I do not find at all attractive. But obviously many people do.