And it should be noted that the colours, which vary between exchange companies, will also vary from area to area. So a red week in a ski area will be at a different time than a red week in a beach area. "Other" could possibly be floating weeks. Some weeks float all year round so they really aren't fixed to a particular colour/season.
Also, within red, you might find references on TUG to weeks ranging from pale pink to scarlet. So for example some beach areas are, according to RCI, red all year round. But a July 4th week is going to be a bright red week, valuable and will get you fairly high trade value, as a general rule. November, pale pink - not a lot of people want to go to the beach in November so it won't be as good for exchanging.
If you're buying something you want to use every year, the colours and exchange values won't mean much to you, just buy what you want and enjoy your vacation. But if you are looking to exchange your week, there's a lot that can be learned before making a choice. This is a very good website to get that education.