I think most of my main characters (whether they are animals in a picture books or teenagers in YA fiction) share a common trait. They are outsiders. Sometimes they are trying to fit in, other times, they just want to be left to their own devices; but in the end they have to stay true to who they are. I believe I'm drawn to this character model, because as a kid I was always just a little too shy, and extremely awkward. Most times, my characters share personality traits of people I know, including myself; but none of them are based on one person.
Although I agree with Monta and Trager, that a characters physical appearance is secondary to their personality, I love it when I can close my eyes and picture the character I'm creating. It helps me feel that I know them a little better. In my YA fantasy novel, my main character is a biracial teenage girl (AA/ Caucasian). Since I don't have a daughter, I image her looking like a teenaged female version of my older son. Brown curly hair, copper colored eyes, tall. Personality wise, she is insecure and awkward. Her abilities cause her emotional angst, but one day, she will learn to use them to her advantage. When I image her, I think of inner and outer traits that comprise a whole being.
The personality of my characters depend on the story I want to tell. I ask myself, how do my characters fit in the world around them? When determining the race of my characters, there's always an internal debate. I have two concerns: one is that if my characters are African American, they may not appeal to a larger audience; the other concern is I don't want to feel that because I'm African American my main characters must always be African American.
Despite these concerns, it is more important to me that my reader is able to relate to my characters. For a little while, I would like my reader to become the person I have created. They should be able to close there eyes and picture the character as I can. If that happens, I have achieved what I have set out to do.