The opacity in the appearance box is set at default. I don't understand why the brown hair is transparent but not any of the skin tones or the males face when they are all on the same layer?
Did you notice that there are two opacities levels shown in the second version? Opacity can be set at the fill level and at the object level as well as the Group level and the Layer level. The opacity or blending mode can be set at any of these levels and may not be apparent unless closely checked. Show a screenshot of the Appearance panel and the Layer panel when the hair is selects, please.
I don't think, that this is transparency.
It's a preview problem. The shapes don't overlap and so anti-aliasing may cause this look.
Turn off anti-aliasing in the preferences and see if the problem is still there.
Any problems just let me know,
Is it possible to do a test print and see if it goes away? I pulled it into CorelDraw, changed view mode to "normal" and it went away. But, outlines will then need to be added to the hair to give it the same look as it has in enhanced view mode. Also, when converting, de-selected anti-aliasing for jpeg export.
Something I do not see in the original file is the pink of her giant bikini shining through her hair (as shown in your screenshot).
What happened to her navel, by the way? It looks like an impatient infant when zoomed in.