The episode title is from an old sailors' mnemonic: "Red sky at night, sailors delight; red sky in morning, sailors take warning." A colorful sunset often portends good weather, while a red sunrise tends to precede a day of bad weather (because weather patterns commonly move from west to east, especially along ocean trade routes). This isn't always true, but it's true enough to be worth remembering.
It also echoes the old shepherds' mnemonic: 'Red sky at night; shepherds' delight. Red sky in the morning; shepherds' warning.' from which the sailors' rhyme was taken. The next episode's title, Red Sky at Night (2010) takes its name from the same place.
This has the first mention of "tiger, tiger". This code word would feature prominently in the sixth season in the buildup to the end of Red John. This comes from William Blake's poem "The Tyger" (as it was originally spelled). In it, Blake explores the question of why such a vicious animal exists, that thinks nothing of killing the innocent (in the poem's case, a lamb), which is a veiled reference to Red John, whose sole purpose of being seems to be the slaughter of the innocent.
Red-haired actress: Leslie Hope.