Black lines/path will not turn white in accessibility high contrast

I've created 2 files in Illustrator. Both files I have saved as a PDF and when I open in Reader/Acrobat I want to change the accessibility to high contrast and invert white to black.

First file - colour lines. Colour inverts fine when high contrast turns on. Black PATHS just turn a dark grey and not white. Black text turns bright white. 

Second file - only black and white lines. Text become white. Lines remain a dark, dim grey.

What setting will make my black lines invert to white instead of grey?