Lord of the Flies by William Golding is set on a tropical island on which a group of English schoolboys gets stranded after a plane accident. Though Ralph, one of the older boys and a leader, wants to keep a signal fire going, the boys just cannot seem to make that happen. Time is passing and things are beginning to fall apart on the island.

Chapter four of the novel is titled "Painted Faces and Long Hair," and it is a chapter full of change, both literal and symbolic.

When a ship passes by the island and the fire has gone out, the boys begin to feel as if it will be a long time before they will be rescued. The "long hair" part of the chapter title refers to time which has passed. Everyone's hair is getting longer (except Piggy's), and this is one of the only ways to mark the passing of time, since the boys were all attending boarding school and had short hair when they landed here. Plus, every day on a tropical island is pretty much the same, so it is important to have markers for time.

Golding writes about Roger's long hair as being "down his nape and low on his forehead," and Jack is also mentioned as having long hair. Ralph's hair is mentioned often, and it is clear that, unlike the others, he finds his long hair annoying and irritating. 

Ralph flung back his hair.

[After swimming, Ralph's] fair hair was plastered over his eyebrows and he pushed it back."

Ralph said nothing. Now both his hands were clenched over his forehead so that the fair hair was kept out of his eyes

It is not surprising that Ralph, more than the others, is unhappy with conditions on the island, including his long hair. The others are devolving into savagery; Ralph is struggling to maintain civility in the midst of savagery.

The "painted faces" portion of the title refers to Jack's painting his face to hunt pigs. He has determined that pigs are seeing him rather than smelling him, so he uses paint to cover his face and trick the pigs. It works, but it is a frightening transformation. 

Jack planned his new face. He made one cheek and one eye-socket white, then he rubbed red over the other half of his face and slashed a black bar of charcoal across from right ear to left jaw.... 

He looked [at himself in the water] in astonishment, no longer at himself but at an awesome stranger. He spilt the water and leapt to his feet, laughing excitedly. Beside the pool his sinewy body held up a mask that drew their eyes and appalled them. He began to dance and his laughter became a bloodthirsty snarling. He capered toward Bill, and the mask was a thing on its own, behind which Jack hid, liberated from shame and self-consciousness.

This is the first indication of true savagery we have in the novel, and this mask of face paint allows Jack to do whatever he pleases, now that he is free from the restraints of shame and conscience. 

Both elements of the title, painted faces and long hair, are literal elements in the chapter which also serve as symbolic elements in the story. 

What is the significance of the title "Painted Faces and Long Hair" in Lord of the Flies?

The significance of the chapter title "Painted Faces and Long Hair" revolves around the symbolism that is developed in the chapter.  At this point in the story, the hunters have decided to use natural resources to paint their faces like warriors.  They smear "paint" on their faces to imitate their imagined view of adult hunters from earlier times.  Figuratively speaking, the boys are at a point when they cover their faces to mask their identities to take on the identities of more evil, sinister characters that are evolving from within their persons.  The painted faces and long hair may symbolically suggest the more "primitive" aspect of human nature that Golding wishes to explore in the novel.