[VoyTech]

Chris, I must have misread your original question. I thought you said something about black and white undersides, and I felt that there was a lot of difference between this scheme and any shade of Sky or pale blue (especially in port view).
Also, I believe (and I suppose Graham will agree) that the difference between Sky Blue and Sky is quite noticeable. Perhaps the two of us put the threshold between "little difference" and "big difference" in a different place than you.
And perhaps it would have been wiser if you had identified the specific angels in your first post before asking which sex they were.