In fact, we will. We will be polite or we will be jerks. Either way, the true color will come out. I guess what I'm hoping is that what we claim on the outside is really what's on the inside. Our actions must validate our claims.
Not too many years ago I acted pretty ugly to a waitress. Then I realized I was wearing a Christian t-shirt with our church's logo on it. I felt ashamed. I should have felt ashamed even without the visual prompting of a t-shirt.
Christians should act like Christians even if we wouldn't get caught acting otherwise. Our normal behavior and first response should honor God. When the heat is turned up or nobody's watching, we should display godly character.
I'm getting better at it but still have a way to go. But God is working on my. He uses lots of tools to make me what I ought to be. Like embarrassment and shame and guilt. He also uses good friends and his Word.
My true colors will show. I want my true colors to be true to God.