I think you're selling yourself short--it's very good so far! The painting metaphor is a good one, and you express yourself creatively. If you're not sure where to go from here, I can make a couple of suggestions.
Unless your teacher specifically told you not to, you might consider talking about a particular person in your own life who has shaped you. This would give you an opportunity to demonstrate, through specific examples, just how that shaping takes place. Have you figured out yet what you want to do with your life, career-wise, and if so, did someone help you make that choice? Or do you play a musical instrument because a particular teacher or performer inspired you to?
If you prefer not to focus on yourself, perhaps you know of someone else, either personally, or through books, television or movies, who had a particularly strong influence in his or her life. I think it's usually easier to write about specific examples than general concepts; that's why I'm suggesting you go that direction.
The strongest piece of advice I can give you is to trust your instincts. You have your own unique writing style and it serves you well. Trust in your own excellence and let the words flow!
I hope this helps!