A child psychologist for a school is asked to see a pupil who draws all
his pictures with black and brown crayons.

He talks to him.  Nothing obvious.  He gives him projectile tests.
Nothing shows up.  Finally in desperation, he gives him some paper and
a box of crayons.

"Oh goody," says the boy.  "I got an old box of crayons in school and
only black and brown were left."