Nissan paint codes can be found under the bonnet on the bulk head (at the back) of the engine bay, other locations are the drivers door at the bottom of the door. Some Xtrail models and Tino models can be found in the footwell under the carpet cut out (near the handle that slides the seat back).
A Nissan Colour Code is typically 3 or 4 digits long, but can also be a letter/number combination.