TIL: Black pencils have a blue base

TIL that black pencil crayons (that’d be coloured pencils to the rest of the world) have a blue base.  And if you use them to darken yellow or orange, you run the risk of ending up w green ;). Suffice to say, I learned this the hard way *sigh* only to have the explanation given shortly after my intended-to-be blond person started sporting greenish hair ;)