What are some of the major themes from chapter 4? And, what is the significance of the chapter title?

Themes in chapter 4 include

The fine line between savagery and civilization. Note Roger is realizing that he will not get into trouble should he actually his a "littlun" with a rock.

The liberation of the savage from their former identity. Jack's mask seems to cut the ties with who he used to be. Jack looks at the “awesome stranger” looking back at him (reflection).

Oh, "Painted Faces and Long Hair" alludes to the fact that they are leaving their old identity of disciplined British school boys behind.