Walnut plank varies considerably in colour.

The sapwood is a pale straw colour, clearly defined from the heartwood which is greyish or greyish-brown, but infiltrations of colouring matter produce a darker-coloured streaky figure to the wood sometimes irregularly distributed throughout the heartwood at other times being concentrated in a relatively small core of inner heartwood.

The darker streaks are usually of a smokey-brown or reddish-brown colour, the decorative appeal often being accentuated by natural wavy grain.