Both Uses

prelude
in
The Fountainhead
(Auto-generated)

The cold washed the colors of the earth, revealing that they were not colors but only the elements from which color was to come, the dead brown not a full brown but a future green, the tired purple an overture to flame, the gray a prelude to gold.†
Chpt 4.3
Which is always a prelude to the age of the cave.†
Chpt 4.19 *

Definitions:

(1) (prelude)
something that comes before and prepares for what follows; in music, a short piece that introduces a larger work or stands alone as a brief, expressive piece (often for piano)

In everyday use, a prelude is an event or action that leads up to something more important, like a small disagreement being a prelude to a larger conflict. In music, the word can mean a short opening piece (for example, before an opera scene) or a short, self-contained work, often written for piano or organ, that sets a mood.
(2) (meaning too rare to warrant focus)