I know this thread is a few months old - but I have recently learned something which is relevant to the original question.
In blue araucana there is an edging to the feather which is not created with the usual lacing genes. It is suspected, but not proven, to be a natural result of melanin placement on the feather. Ergo you have a "naturally occurring" edging.
So what we see are blue birds with blue "edgings". Here's an example - one of my young blue araucana I bred this year.
View attachment 2873804
It therefore seems logical that if you removed the effect of the blue gene - you would then get a black feather with black edging.
This supports the original posters comments as to why she can see faint edgings on the black feathers!!