Well I did some investigating, and it turns out there is a whole science behind this phenomenon, and you can actually tell a lot about someone by their favorite color.
Yellow: The color of happiness, wisdom, and imagination, Yellow is chosen by the mentally adventurous, searching for novelty and self-fulfillment. Yellow usually goes with a sunny and shrewd personality, with a good business head and a strong sense of humor. It is the color of intellectuality and all things to do with the mind. Yellow folks are usually clear and precise thinkers who have a good opinion of their own mental capacities and who have lofty ideals. They may at times tend to shun responsibility, preferring freedom of thought and action.
Now you may not buy into the whole color theory but...good business head, strong sense of humor, intellectuality, freedom of thought and action... I gotta be honest, but if someone had just shown me a list of these attributes, my first guess would have probably been Hillary Clinton.
This is definitely a science worth looking into.