the blue crayon is typically the most used crayon in a box... therefore a person who is a blue crayon is used...a lot...and well, basically it's just a nice phrase for slut.
Fogey/fogy /fougi/ sl. (early 18C+, orig. Scot) old-fashioned, stuck-in-the mud.
Person with old fashioned ideas which he is unwilling to change: Come to the disco and stop being such an old fogey!
You think me an old fogeyand an old tory, his thoughtful voice said. I saw three generations since OβConnelβs time. I remember the famine. Do you know that the orange lodges agitated for repeal of the union twenty years before OβConnel did or before the prelates of your communion denounced him as a demagogue? You fenians forget some things. (James Joyce, Ulysses. Penguin Books,1992. p. 38)