If yellow is brought by a healing agent, a supportive, helpful character in the dream, it means you have difficulty rationalizing or are timid with regard to the subject matter of the dream. The healing agent brings yellow to help you rationalize your fears. An irrational fear, like a fear of spiders, has no valid basis and never helps you in life.
If a guide wears or brings pure bright yellow then you have an intuitive or enlightened intellect - yellow (intellect) plus white (enlightenment). You are being asked to use this to gain an enlightened perspective on the subject matter of the dream. To dream of pure bright yellow on its own is also sufficient to indicate you have this ability.