I will aswer that, but as usual you will not believe me, but maybe Tim can back me up here... and then you will believe him LOL...thanks so much. That makes since. I breed my lavender ameraucana roo to my rhode island white hens and those had black feathers here and there. I wonder why. Should all black be void or just in the tails and wings.
The Lavender Ameraucana roo is based on Extended Black with recessive lavender making him look self lavender(solid lavender body), your RIW female is wheaten Based and Dominant white, when you make this cross you will ber E/eWh I/i+ birds, and since Dominant white is not completely dominant, meaning is a leaky gene(will leak gold and black feathers) you had a mostly white bird with some black leaking...
does that makes any sence? or maybe Tim will explaint it better, he is a better Teacher after all