Candor usually means the quality of being open, honest, and sincere. If someone tells you they think you're boring, you might reply with, "While I appreciate your candor, I don't think we need to be friends anymore."
The corresponding adjective is candid, as in "I want you to be candid. Did everyone notice the spinach between my teeth when I gave my speech?" Candor is from French candeur, from Latin candēre, "to shine or be white." The color white is associated with purity, which is a now obsolete meaning of candor.