There is no standard for wire colors on 3-way switch travelers. The colors will vary depending on whether NM cable or conduit was used.
With NM cable, the wire colors for travelers will be black and red using 3-wire cable.
With conduit, the wire colors for travelers could be any color. In the 2nd diagram below, blue wires are used for travelers.
Line voltage enters the light fixture outlet box. No longer allowed after 2011 NEC (if no neutral wire in switch boxes)
Line voltage enters the first 3-way switch outlet box, light fixture is located between switch boxes. No longer allowed after 2011 NEC (if no neutral wire in switch boxes)
Black common wire is usually wrapped around the two traveler wires on a 3-way switch.
Alternate 3-Way Switch Wiring Diagrams 1, NM
Typical 3-Way Switch Wiring Diagrams, NM Cable
With conventional wiring, line voltage enters the first 3-way switch box
3-Way Switch Wiring Diagram Example, Conduit
Alternate 3-Way Switch Wiring Diagrams 2, NM
Typical 3-Way Switch Wiring, NM Cable
In the 1st diagram below, a 2-wire NM cable supplies power from the panel to the first switch box. The black (line) wire connects to the common terminal of the first 3-way switch. A 3-wire NM connects the traveler terminals of the first and second 3-way switch together. Traveler wires are interchangeable on each switch.
The common terminal of the second 3-way switch connects to the light fixture(s).
The white neutral wires are connected together in each switch box.