There is no standard for wire colors on 3 and 4-
With NM cable, the wire colors for travelers will be black and red using 3-
With conduit, the wire colors for travelers could be any color. In the 2nd diagram below, blue wires are used for travelers.
In the 1st diagram below, a 2-
The common terminal of the second 3-
The white neutral wires are connected together in each switch box.
Diagrams shown on this page are simplified for clarity. Electrical outlet boxes can have numerous NM cables going in and out. See Actual Switch Box Wiring Diagram.
Ground connection diagram is shown separately.