She identifies the colour white with the sun, warmth and light; that is why she uses flour to make her face white. By this stage in the movie the audience is fully aware of Ruby's mental instability and her terror of the dark. That is why her journey is so remarkable: to be out after dark requires a supreme act of will.
She associates white with the sun, warmth, and light; hence she uses flour to whiten her face. By this stage in the movie, viewers are aware of Ruby's mental instability and fear of darkness. This explains why her nighttime journey is so remarkable: it requires a powerful act of will.