I seem to remember from the distant past. When timber was loaded on ships .That the colours used to be a indicator of where the timber came from, and it's destination. This helped ensure that the logs or packs of timber were stowed in the correct order, for discharge at the relevant ports, and that the individual receivers received all the timber they had paid for. It's years since I have had anything to do with stowing timber on ships, and things may have changed.