Yellow Pages Definition

noun

A volume or section of a telephone directory that lists businesses, services, or products alphabetically according to field.

American Heritage

The section or volume of a telephone directory, usually printed on yellow paper, containing classified listings of subscribers according to business, profession, etc.

Webster's New World

A telephone directory that lists commercial organizations.

Wiktionary

Origin of Yellow Pages

So called because they are usually printed on yellow paper

From American Heritage Dictionary of the English Language, 5th Edition
From such directories being printed on yellow paper

From Wiktionary