Multi-pair phone and data wire uses an industry-standard color code to distinguish one pair from the others, and to identify the wires within a pair. Each wire usually has a base color and a contrasting stripe, and the other wire in the pair has the opposite colors.
The first pair of wires in a multi-pair cable usually has a white wire with blue stripes, and a blue wire with white stripes. There are codes for 25 different pairs.
The first wire in a pair is traditionally identified as "tip" and has positive voltage. The second wire in a pair is called "ring" and is negative. The tip and ring terminology refers to the construction of the plugs used in old-fashioned "Lily Tomlin" switchboards.
What normal people describe as "gray" is traditionally identified as "slate" in the phone business, to avoid confusion caused by a "GR" abbreviation which could be either green or gray.
What most people describe as "purple," is traditionally called "violet" in the phone business. We don't know why "PU" isn't used for purple. Maybe people think "PU" smells bad. (Diagram from Leviton)