You have all four temperaments but almost always one is dominent or the strongest. It is the one you tend to use most.
Exercise: Write you name on a piece of paper. Think about that experience. It probably was so automatic that you may wonder what there was to think about it. After some consideration you might say it felt comfortable, didn't take any thought, it was easy to do, etc.
Explanation: Very likely you used your dominant hand to write your first signature. Most people are right-handed while only about one in seven are left-handed. Assuming you were allowed to choose which hand you could use for writing, then that hand was your dominant hand. The other hand was your non-dominant hand. So it is with your temperament. One colour tends to be dominant and that is the one you automatically use, but there are situations in which another temeprament would work better for you so you might use that one instead. Temperaments aren't nearly as rigid as handedness. Some people are useless with their non-dominant hand; however, there are a few people who are ambidexterous, i.e. can use either hand with equal ease. It is a similar case with temeprament. Some people seem to only use one temperament while most people can switch temperaments with ease. You may be able to choose which temperament to use, but usually it just occurs automatically and without conscious thought.
How about having more than one dominat temperament? It sounds like it might be good to be equally able to use any of the four temperaments. The difficulty is that in every situation you would have to decide which temperament to use. It would be like facing in four directions at once. It would be better to have one dominant temperament that comes up automatically, but have the other temperaments available to you when you need them.
Is it important to develop the other three temperaments? Being able to switch from one temperament to another would be quite useful. Suppose you are a Dependable Gold. Your friends call and say lets go down to the mall. Your Dependable Gold thinks of all the chores that you have to do and could do. But then you think of how you have been working hard for such a long time and need a break. Now it would be helpful to be able to turn on your Action Orange and go off and have some fun. Your Dependable Gold is probably ticking away in the background warning you when you have stayed away too long, but all in all you had a great day and you are now ready to get back to work.