I believe in the the correspondence theory of truth. That simply means that truth is that which really is. If something conforms to reality, it is true. If not, it is false.
Truth is not merely cultural. A sunny clear sky at noon on earth is blue no matter what your culture teaches and no matter what word is used to mean "blue" in your language. Asserting that you believe the sky is yellow just indicates that you are wrong. It is not open-minded for me to claim that you have your truth and I have mine about the color of the sky--rather, it is merely empty-headed.
Although common sense should point to the correspondence theory of truth as the only realistic possibility, many seemingly intelligent people oppose it. Somehow they must support views which can only be self-defeating, since you can't get very far promoting a concept of truth that does not comport with reality.