To use DaHai8's plugin on a mac:
Step 1) Download the plugin here: http://bitman.org/dahai/WoodGrain.zip
Step 2) Unzip and place WoodGrain.py in the following dir:
/Applications/Cura.app/Contents/Resources/plugins/plugins/PostProcessingPlugin/scripts
Step 3) Re-Launch Cura and select:
Extensions --> Post Processing --> Modify G-Code
Step 4) Click "Add a Script" --> "Wood Grain"
Step 5) ¯\_(ツ)_/¯
Step 6) Profit