The different colors could mean a lot of things. I personally think they change the colors from the previous cruise as not to mix up the outgoing luggage and the incoming ones?? Just a guess, but I also thought that for a certain sailing, all the tags were the same color and you have to put your cabin # , Name etc on them.
Since you don't know what cabin you will be in yet, keep in contact with your travel agent. The agent may get a cabin number before you cruise and you can completely fill out the luggage tags. Only put the tags on the luggage that you will be checking in at the airport.
Was on Ocean Princess earlier this year and absolutely loved the ship, I'm sure you will too, enjoy!