So you work from the common ground: "You probably know I can't see the blue people, but I can see that you're bleeding. Can I help you with that?"
It works, more often than not. Not just here, either.
Talking to a friend recently about cultural sensitivity instruction. Many do it backwards, to my mind. They try to give you a list of all the ways that all of the world's different cultures differ from yours. Sometimes without even knowing what your culture is.
It backfires, sometimes. There is nothing quite as annoying as someone who watched a television special on a part of the world and feels a need to tell a native what that native believes and why. The whole time, the speaker feels 'sensitive.'
Work from the common ground. Respect is actually pretty universal. So is truth. I've never insulted anyone by saying, "I know absolutely nothing about your country. How do I say, 'Hello'?" There is no disrespectful way to ask for instruction, as long as you are sincere, and follow it up with actually listening and learning.
Cultural differences, mental health, even politics and religion. All easier to understand starting from the common ground.