A shade is what one ends up with when black (or some other dark color) is added to a pure hue. Suppose you had some green paint and mixed a bit of dark gray paint into it. The resulting paint would be darker than (also known as a shade of) the original green. Think of a dazzlingly sunny day with intense color all around, then picture the way the light and colors change when you place yourself under the leafy shade of a tree.
