You can say: Why does a character in a film with the name "Violet" have (such) a hideous and unreliable personality? Violet is simply the name of a flower, and also the name of its color. The color violet is like purple. I don't think there are any common connotations of this name. You should know that in literature and film, things can be ironic. Like a very big man who is named "Tiny". Violet is simply a female's name, so it could have no relationship with the person's character. (Note that in english, the word "character" has more than one meaning. In the previous sentence, it means 性格. In a film or a book, it's 角色, like in the first sentence of my reply.)

Violets are a symbol of faithfulness. Blue violets say "I'll always be true" and signify constancy White violets depict modesty or the desire to "take a chance on happiness Yellow violets convey modest worth. Often a girl who was very shy was described as a "shy, retiring violet" The name Violet is very old fashioned, popular during World War 1 and 2.

I associate people who are named Violet as people who are fruity :P