White-winged or Yellow-chevroned?

As a birding professional has taught me, "The primary way to separate the two is by looking at the face.  On a White-winged parakeet, the face is 
sparsely feathered and shows mostly grayish skin. On a Yellow-chevroned Parakeet, the face is fully feathered.  Additionally,  the Yellow-chevroned Parakeets are  more "grassy-green" color compared to the darker green of a White-winged."