In psychology the color yellow is related to mind and intellect, it has a positive and a negative connotation. Positive: optimism, cheerfulness, enthusiasm, fun, good-humored, confidence, originality, creativity, challenging, academic and analytically, wisdom and logic. Negative: being critical and judgmental, being overly analytically, being impatient and impulsive, being egotistical, pessimistic, an inferiority complex, spiteful, cowardly, deceitful, non-emotional and lacking compassion. Here it seems that the writer is using the negative connotation.